TOEFL tests a test-taker’s ability to use and comprehend the English-language in the academic environment. In the academic environment, English is formal and sophisticated. It means that you can’t speak or expect your teachers to speak using slang.
The new TOEFL does not test your vocabulary objectively. In other words, you don’t have to write meanings, antonyms or synonyms. Your goal then is to build vocabulary in such a way that it would help you to comfortably understand the text passages, extracts, and lectures that are taken from the academic sources.