On the ASVAB Word Knowledge subtest, if you do not know a word and cannot decode it, what is the best approach?

The ASVAB does not penalize wrong answers, so you should never leave a question blank. The best strategy for an unknown word is to first eliminate any choices you can tell are wrong — including obvious antonyms or words unrelated to the apparent meaning — then guess among what remains. Decoding by prefix, root, and suffix can also narrow the options. Because a blank scores the same as a wrong answer (zero) but a guess has a chance of being right, answering every question maximizes your score. Strategic guessing after elimination is a key vocabulary tactic.