Lucas has already introduced you to the prefixes “in-“ and “pro-.” Let’s look at three more prefixes that you’ll need to know for the TOEFL: “un-,” “under-,” and “inter-.” These prefixes have similar spellings and sounds, but distinctly different meanings.
Meaning: “Un-“ means “not.”.
1) We will probably never be able to carry on unaided conversations with cetaceans. (Source: Official TOEFL iBT Tests)
“Aided” means “helped,” so you can know that “unaided” means “not helped.” The sentence is saying that without some kind of artificial help, humans will never be able to talk to cetaceans. (Cetaceans are the highly intelligent class of sea animals that includes dolphins and whales.)
2) Earth is a target in a cosmic shooting gallery, subject to random violent events that were unsuspected a few decades ago. (Source: The official ETS website)
To “suspect” something means to have an idea that something is true before you have seen evidence or proof of the truth. Combine that with “un-,” and you can guess that “unsuspected” means “true, but not known or believed.” The sentence states that until recently, no one thought that the earth had suffered random hits from meteors and other objects from outer space.
Meaning: “Under-“ means “beneath,” “below,” or “not enough.”
1) Another very common strategy sets an initial price low. Now this happens when the market is already saturated with the product and the strategy is to undercut its competitors. (Source: The official ETS website)
We know that “cut” can mean to hurt or wound a person or thing. Businesses are at odds with their competitors, so this meaning of “cut” makes sense. A business is trying to benefit itself at the expense of its competitors. “Undercut” must mean “to damage competitors by going underneath them.” Going underneath the competitors how? By selling the product at a lower price than they do, as indicated in the first sentence in this sample.
2) Nearly any kind of plant of the forest understory can be part of a deer’s diet. (Source: Official TOEFL iBT Tests)
“Story” can mean “a retelling of a series of events,” as in a news story or a children’s storybook. That meaning doesn’t make sense in the sentence above. “Story” can also mean a single floor of a building, as in a ten-story apartment building or a third story office. By looking at the second definition, you can easily guess that the “understory” of a forest is the floor of the forest beneath the trees.
Meaning: “”Inter-” means “between” or “together.”
1) Our loan period is a month. Oh, I should also mention that we have an interlibrary loan service … if you need to get hold of a book that’s not in our library. (Source: The official ETS website)
“Library,” as you probably know, means “a collection of books that people can borrow.” (Occasionally it simply means “a collection of books.”) It can be inferred that “interlibrary” means “between libraries” or “libraries together.” In fact, in means both of these things. “Interlibrary loan” means the “lending of books between one library and another,” which is something that happens when libraries work together.
2) Interbedded with the salt were thin layers of what appeared to be windblown silt. (Source: the official ETS website)
“Bedded” means “laid down.” Thus, you can assume that windblown silt (“silt” is sand, dirt, and other particles carried by wind or water) is laid down together with the salt.
It’s easy to confuse “un-,” “under-,” and “inter-.” If you think you see the prefix “un-“ in a word you are not familiar with, look at the letters carefully. You want to make sure you are not just reading the beginning of “under-.” Similarly, be prepared to quickly spot the spelling difference between “under-“ and “inter-“ on the timed reading tasks in the TOEFL.