means a statement or situation that seems to contradict itself yet may be true, or that defies intuition by holding two incompatible truths at once.

from From Greek 'paradoxon,' a thing contrary to expectation — built from 'para' (beside, beyond) and 'doxa' (opinion, belief). So at root a paradox is what stands 'beside belief,' just off to the side of what we expect to be true. It came into English through Latin in the 16th century.