an·tith·e·sis / anˈti[unvoicedth]əsis/ • n. (pl. -ses / -ˌsēz/ ) a person or thing that is the direct opposite of someone or something else: love is the antithesis of selfishness. ∎  a contrast or opposition between two things. ∎  a figure of speech in which an opposition or contrast of ideas is expressed by parallelism of words that are the opposites of, or strongly contrasted with, each other, such as “hatred stirs up strife, but love covers all sins.” ∎  (in Hegelian philosophy) the negation of the thesis as the second stage in the process of dialectical reasoning. Compare with synthesis.

ANTITHESIS [Stress: ‘an-TI-the-sis’].
1. In RHETORIC, a construction in which words are opposed but balanced: ‘For many are called, but few are chosen’ (Matthew 22:14); ‘To err is human, to forgive, divine’ (Pope, 1711). Technically, the first part of such constructions is the thesis (‘for many are called’), the second the antithesis (‘but few are chosen’).

2. In general usage, opposite: This policy is the antithesis of everything we believe in. See CHIASMUS.

antithesis XV. — late L. — Gr. antíthesis, f. ANTI- + tithénai set, place (cf. THESIS).
So antithetic XVII, antithetical XVI. ult. — Gr. antithetikós.