Doing well on the GRE verbal goes far beyond just knowing obscure words. The test writers reward those who can understand complex text and make valid inferences about this text. Of course, it doesn’t hurt to have a strong vocabulary; but that will only get you so far.
Nonetheless, there may be that one Text Completion in which the correct answer hinges on the difference between two words, one a word that you know pretty well and one that you’ve never seen before. For example:


The modern antibiotic assault on “bugs” has been effective at eliminating much deleterious bacteria. Yet in not (i) _______ such bacteria, antibiotics have allowed that which remains to proliferate, thereby making antibiotic-resistant bacteria more (ii) _______.

Blank (i)	Blank (ii)
A) pinpointing	D) undetectable
B) extirpating	E) common
C) animating	F) percipient

Now, I’m assuming that you already have a very strong vocabulary and that you’ve gone through most GRE words. If you haven’t, the words below aren’t really worth your time—they’re that uncommon. Those looking to move on to the hardest verbal section, however, should be familiar with these relatively obscure words. They might be the correct answer, or they might be a tempting distractor (test-speak for wrong answer).
As for the Text Completion above, take another crack at it once you’ve learnt the words below.

Manumit

A word that is mostly used in historical contexts, manumit means to release from slavery or liberate. The opposite would be to subjugate. Manumission is the noun form of manumit—I’m guessing I should throw that in there since it looks so different from manumit.

Percipient

Want to know a fancy way of saying perceptive, one that nobody really uses these days? No? I don’t blame you. But the GRE might throw percipient at you.

Farrago

Nope, this is not a town in North Dakota, or a movie with the same name. A farrago is a confused. jumble of things. The focus is in on disorder. This list is a farrago of words, not surprisingly, given my loose theme: relatively obscure words.

Lambent

This word does not relate to a wooly quadruped. There are two definitions: flickering light that glows softly, and lightly brilliant wit. It’s a pretty poetic word that might end up in one of the passages or in a Text Completion that features a poetic voice.

Extirpate

There were once two words that meant the same thing. One said to the other: there is only room for one of us. And like that, eradicate and extirpate become locked in mortal combat, and only eradicate emerged victoriously, having extirpated extirpate, as it were. To eradicate, by the way, means to completely eliminate or remove any trace of.

Deracinate

A similar word to extirpate, though no bloody battle involved, deracinate means to pull out by the roots. But here the focus is not on eliminating but displacing. Immigrants forced to flee their countries during wartime have been deracinated.

As for the Text Completion above, the answers are (B) and (E). (A) is close but not quite—the sort of subtly you might see test day.