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ACT Vocabulary | Words You Must Know


Many students are confused about ACT vocabulary and what types of words they need to know. Is ACT vocab similar to SAT vocab? What's the best way to study ACT vocabulary?

In this article, we break down exactly how the ACT tests vocabulary, go over the words it tests most often, and give you tips on how to approach vocabulary on the Reading and English sections. As a bonus, we also offer a list of our top 15 ACT words and a free study sheet of our top 150 ACT words!


How Is Vocab Tested on the ACT?

Our modern idea of vocabulary in terms of academic testing comes from the College Board's almost 100-year-old approach to it. In 1926, the first SAT included 33 of these rudimentary fill-in-the-blank vocabulary questions:



See the end of this post for the answers to this vocab question and others!


These fill-in-the-blank questions are why (for as long as most of us can remember!) students have prepared for tests by memorizing definitions. This is because it's easy to score high just by cramming 100 definitions into your brain.

But ACT, Inc., and the College Board soon learned that knowing the definition of a word is not the same as knowing how to use it effectively in a sentence. 

For example, the dictionary definition of engender is "to cause." But a student who only knows the definition might think engendered belongs in the following sentence:

"The harsh professor _____ the sensitive student to cry."

The problem here is that engender actually means something between "encourage" and "cause." It'd be weird to say that a professor encouraged a student to cry, wouldn't it? Instead, it's better to say that the harshness itself engendered something.

In addition, engender can only be followed by a noun, so it'd be correct to say something like this:

"The professor's harsh tone engenders a tense classroom atmosphere."

As you can see, a word's use in the context of language is just as important as its definition. Most big tests have caught onto this, including the ACT and finally the SAT (as of 2016).

But the ACT takes an even subtler approach to testing vocabulary, including it where knowing the word is absolutely crucial to understanding or answering a question. Vocabulary words on the ACT are usually surrounded by several hints to their meanings. These hints are also known as context clues, and we'll talk more about those next.


The ACT Loves Context: Clues and Vocabulary

As we discussed earlier, knowing definitions of words isn't as good a measure of language mastery as is the skill of choosing the best word for a specific context. In other words, it's less about the words themselves and more about how they fit with the words around them.

The ACT really takes this to heart and rewards students who know how to use context clues. Here's an ACT question that targets vocabulary:


The difficult words in the question above are sound and intact, which both mean undamaged, but this is only part of the question. The word total seems like it fits into the list of words, but when we insert it into the sentence, it reads "the feather is total," which is clearly wrong. So we need to know that sound and intact mean something like "whole," but there's other information (context) that helps us answer the question.

Here's another interesting ACT example. The highlighted words are the ones that you need to know to get the question right with 100% certainty.


With this tougher ACT English question, we need to know that emphatic means "expressing something forcibly and clearly" in order to choose correctly among the options. Only one choice (asserts) is even close to this definition, but it's also a tough word for many students.

However, if we know emphatic, then we know that hints, supposes and probably says aren't strong enough. Again, in this ACT question, we have some leeway with our vocabulary skills.


What Kinds of Vocab Words Does the ACT Test?

We now know that the ACT has a very specific, context-focused approach to testing vocabulary. In general, the words tested on the ACT are similar to those on the SAT. Here are the five defining qualities of ACT vocab words:


#1: The ACT Only Tests Medium-Level Vocabulary, but Tests It in Detail

When you look at the Top 15 ACT Words at the end of this article, you might already know many of the words. That's great!

However, make sure you really know what these words mean. By this, I mean look them up and read them in a few different sentences to be sure you understand how to use them correctly.

While the ACT doesn't test super difficult vocab words such as abstemious, crepuscular, and blunderbuss, it does test the nuances of more common words such as adhere, cumbersome, and diffuse. Many of these nuances include multiple meanings, which we'll delve into next.


#2: The ACT Loves Words With Multiple Meanings

The ACT likes to test secondary (less well-known) or academic meanings of ­­words. Let's look at a few examples from real ACTs.

First off, what do the words determined and critical mean to you? You probably thought of the most common definitions of these words: determined is an adjective meaning persistent, while critical is an adjective meaning disapproving.

But both of these words also have secondary, more academic meanings. Determined, for example, is also the past tense of the verb determine, which means "to establish something exactly." Here's an example of this particular usage:

"In the 16th century, Nicolaus Copernicus determined that the Earth revolves around the Sun."

Determine, used in this way, is one of the most common vocabulary words on the ACT.

By contrast, critical is always an adjective (most words ending in "al" are), but it still has multiple meanings. While the more popular meaning of critical, "disapproving," describes a person, the academic meaning refers to an analysis or explanation of something, as in the following example:

"The scholar's critical analysis of Macbeth shows that Macbeth's greed is the main cause of the play's events."

One trick you can use on the ACT is to think of unknown words metaphorically.

For example, the word cumbersome technically means "large or heavy and therefore difficult to carry or use." But it's actually more often used to mean "slow or complicated and therefore inefficient."

Now, let's look at an ACT Reading example in which we can apply this strategy.


Let's say we think the answer to the question above is F, but we don't know what self-absorption means. We know that absorb means to soak up or take in, and we know what self means.

If we think of absorb in a metaphorical way—soaking in one's emotions or thoughts, rather than literally absorbing liquid with a paper towel—we might be able to guess that self-absorption means being absorbed by oneself and not focusing on anything external.

This tactic can be applied to many multiple-meaning words tested on the ACT.


#3: The ACT Loves Idioms

Another way the ACT tests language skills is through idioms—that is, phrases that mean something different than what the actual words mean. For example, "bite the bullet" is an English idiom that means to do something that's difficult to do. It doesn't have anything to do with biting or bullets.

Here are a few idioms from recent ACTs:

  • hush-hush: secret
  • under wraps: secret
  • streak past: go past quickly
  • came about: happened
  • in the midst: during
  • sheds light on: reveals, explains
  • ill at ease: uncomfortable (mentally, not physically)
  • dwell on: focus on for longer than necessary
  • against the clock: under time pressure
  • stumbled upon: discovered by accident

It's difficult to study idioms as there are thousands of them in English. Luckily, the ACT only tests idioms that are widely used, so an easy way to improve your idiom knowledge is to read, read, read.

If you come across a phrase that doesn't make sense, ask your teacher or another adult to explain it to you since idiom definitions can be difficult to find reliably on the internet.


#4: The ACT Includes Science Vocabulary

Lots of people freak out about ACT Science, but it's really quite straightforward—if you're familiar with science. There are difficult topics and vocabulary, such as heritable traits and conductivity, but the test clearly explains all of these concepts. That said, you'll have to know or be able to work around the more general and vague science terms. 

One thing that can make ACT Science less scary (especially if you haven't taken chemistry or biology) is to make sure you know some basic scientific ACT vocabulary words. The vocabulary list attached to this article includes almost 40 science vocabulary words for just this purpose.

It can also be useful to read articles in scientific publications, such as Popular Science, Discover, and the science section of the New York Times.


#5: SAT Vocabulary Looks a Lot Like ACT Vocabulary

In 2016, the College Board promised to make the SAT more relevant to college success. This meant getting rid of a bunch of obscure words such as lachrymose (tearful, sad) and ushering in college-level words that are more frequently used in academic texts. As a result, SAT vocab words are now extremely similar to ACT vocab words.

Each of the top 15 ACT vocab words below can be used broadly to discuss various academic topics and are likely to appear on the SAT as well.


PrepScholar's Top 15 ACT Vocab Words

The ACT uses a lot of the same vocabulary words over and over. Unsurprisingly, these words relate strongly to literary and scientific topics, and have variations (italicized and in parentheses below) that are also important for the test.

You might notice that many words have multiple meanings; our extended Top 150 ACT Words list tells you which meanings are most likely to appear on the ACT.

These are the words you absolutely must know!

  1. analyze (v.): to examine in detail, typically for purposes of explanation and interpretation

    (analysis, analytical)

  2. compose (v.):
    1. to write or create
    2. to constitute, make up

      (composition, composed of)

  3. correlate (v.): to have a mutual relationship or connection

    (corollary, correlated)

  4. critical (adj.):
    1. expressing adverse or disapproving comments or judgments
    2. expressing or involving an analysis of the merits and faults of a work of literature, music, or art
    3. involving the objective analysis and evaluation of an issue in order to form a judgment
    4. (of a situation or problem) having the potential to become disastrous; at a point of crisis

  5. determine (v.):
    1. to cause (something) to occur in a particular way; to be the decisive factor in
    2. to ascertain or establish exactly, typically as a result of research or calculation

  6. differentiate (v.):
    1. to recognize or ascertain what makes (someone or something) different
    2. (differentiate between) to identify differences between (two or more things or people)
    3. to make (someone or something) appear different or distinct
    4. to make or become different in the process of growth or development

  7. engage (v.):
    1. to occupy, attract, or involve (someone's interest or attention)
    2. (engage someone in) to cause someone to become involved in (a conversation or discussion)
    3. (engage in) to participate or become involved in

  8. emerge (v.): to become apparent, important, or prominent

  9. evolve (v.): to develop gradually, especially from a simple to a more complex form

  10. infer (v.): to deduce or conclude (information) from evidence and reasoning rather than from explicit statements (inference)

  11. omit (v.): to leave out or exclude (someone or something), either intentionally or forgetfully

  12. precede (v.):
    1. to come before (something) in time
    2. to come before in order or position (preceding)

  13. redundant (adj.): not or no longer needed or useful

  14. reflect (v.):
    1. (of a surface or body) to throw back (heat, light, or sound) without absorbing it
    2. (of a mirror or shiny surface) to show an image of
    3. to embody or represent (something) in a faithful or appropriate way
    4. (reflect well/badly on) to bring about a good or bad impression of; Ex. The incident reflects badly on the operating practices of the airlines.
    5. (reflect on/upon) to think deeply or carefully about

  15. relevant (adj.): closely connected or appropriate to the matter at hand (antonym: irrelevant)


2 Quick Tips for Studying ACT Vocab

To help you get down these15 ACT words (and any others you might come across!), make sure to try our quick tips below.


#1: Use Flashcards and the Waterfall Method

By far the fastest and most effective way to learn ACT vocabulary is to make and use flashcards.

In particular, you'll want to use the waterfall method—an easy way to help you memorize words and their definitions fast. With this method, you'll go through your deck one card at a time so that you can ultimately spend more time studying words you don't know (versus those you do know).

Not a fan of paper flashcards? No problem. Try downloading Anki, a free computer program that uses spaced-repetition software (SRS) to show you trickier cards more often than easy ones.


#2: Take Official ACT Practice Tests

Once you've memorized these 15 ACT vocab words (and any other words you find along the way), it's time to put what you've learned to the test by taking an official ACT practice testThese tests are just like the real deal and offer you the best, most accurate ACT vocab practice possible.

Some words of caution, though. For one, take the practice test in a quiet place, preferably where you won't be disturbed by anything, such as a library. Secondly, make sure to time yourself in accordance with the actual time limits on the ACT. This way you can slowly build the endurance you'll need for test day!


Answers to the Questions in This Article:

  • (28) economics
  • (29) cellulose
  • (30) homeopathy
  • (63) C. total
  • (73) D. asserts
  • (28) F. deceptive self-absorption


What's Next?

Want more tips for studying ACT vocab? Then learn about the waterfall method—the best way to memorize vocab words. Though this guide talks specifically about SAT vocab, the method can be applied to any and all vocab words you study!

Wondering whether you should take the ACT or SAT to get into college? Read our breakdown of which test is easier and learn about the major differences between the ACT and SAT to help you decide which test is right for you.

What's a good ACT score, and what score should you aim for? Jump into our step-by-step guide to figure out your ACT score goal and how you can reach it.



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Laura Registrato
About the Author

Laura has over a decade of teaching experience at leading universities and scored a perfect score on the SAT.

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