You don’t need to learn a lot of unusual or difficult vocabulary words to succeed on the SAT. Instead, the words you’ll be asked about are words that come up often in college-level reading and professional life.
The SAT also doesn’t ask you to supply the definition of a word without any context to guide you. All of the words you’ll be asked about will appear in the context of reading passages, so you can use context clues to guide you to the best answer.
That said, it’s worthwhile to take the time to build your vocabulary by learning the meaning and usage of the words that appear most often in college-level assignments. If you do, you’ll have a much easier time with the test because you won’t have to spend time guessing from context clues what a word might mean. Your sight recognition of vocabulary words will help you read passages faster and with greater confidence.
You should also practice identifying the meaning of words in context with Official SAT Practice on Khan Academy®.