Although analogies were removed from the SAT in 2005, vocabulary continues to figure prominently both on the exam and in the minds of the students who take it. Words that once populated analogies have in many cases snuck across the page to constitute answer choices for reading comprehension questions. So, thinking underscore and undermine are synonymous may leave you bereft! Even more problematically, the PSAT and SAT routinely feature a series of questions that all focus on a particular paragraph or sentence, often a nasty one. Not knowing mollify and therefore the sentence that hinges on it may wipe twenty or thirty points from your score.
More broadly, comprehending reading is darn tough if you don't understand individual sentences and understanding individual sentences hinges on knowing the words that comprise those sentences. Granted, we all have the ability to discern the meaning of an unknown but familiar word from context but that has its limits. Don't know one word in a sentence? That's probably fine. Two? Might start to make things fuzzy. Three? Now you are starting to see this sentence as though you are reading Camus while in third year French! At the very least, having to figure words out by context slows you down as you need to read and reread a sentence, and likely the previous and successive sentences as well. And that can't be good for your pacing or your confidence.
Moreover, sentence completions still account for roughly a quarter of the questions. A single PSAT sentence completion on last year's exam had answer choices of demographic, temporal, filial, tacit, and prescient. Gulp. Still think you can figure things out by context? So, if you are serious about the PSAT and SAT, you should be serious about knowing and learning words. Make it part of your routine. Pay attention to words you do know and make it your habit to look up and learn the ones you don't yet know. Words do matter..