The TOEFL tests vocabulary in several ways, none of which are ways you’re probably used to being tested in English classes. Although there are overt (direct) vocabulary questions in the reading section, vocabulary is equally important in every section of the test.
Vocabulary in the reading and listening sections
The reading section is the most challenging section in terms of vocabulary, and it’s also the only one where you’ll be asked outright to define a word from the passage. For the most part, you’ll just need to be able to navigate the passage and understand what it’s saying, so if you don’t understand every single word, you’re probably still fine. You can expect a handful of vocabulary questions, though. Sometimes, you can figure out the meaning of the word from context if it’s unfamiliar, but mostly, these questions depend on whether or not you already know the words used.
Of the unfamiliar words you encounter in the reading section, some will be technical words that you don’t need to know. When you see a really complicated, advanced-looking word, don’t panic! It might be hyperlinked, and clicking it will show the definition on the lower left side of the screen.
For most people, the listening section is be the least difficult section in terms of vocabulary. Learn the critical language for talking about academic life (words about things that happen at universities, such as “thesis paper” and “academic advisor”), and then focus on understanding the subtext, or the implied meaning, of speakers’ words.
Vocabulary in the writing and speaking sections
The highest score on the Speaking section rubric has this to say about the use of vocabulary: “The response demonstrates effective use of grammar and vocabulary.” If you move down a level to a score of 3, then the “response may exhibit some imprecise or inaccurate use of vocabulary or grammatical structures or be somewhat limited in the range of structures used.”
Getting a top score on the independent writing task requires “consistent facility in the use of language, demonstrating syntactic variety, appropriate word choice, and idiomaticity, though it may have minor lexical or grammatical errors.”
If you score one point lower, then you also showed a wide range of vocabulary, but also had “occasional noticeable minor errors in structure, word form, or use of idiomatic language that do not interfere with meaning.”
I quote these rubrics not because I like big, fancy words (although I do), but because they make a very important point: in these sections, vocabulary is tested not in terms of what you don’t know, but in terms of what you do. You need to be able to express yourself fully without repeating yourself to get full marks, but generally speaking, you can use any word that suits you—you won’t be encouraged or expected to use a particular one.