noun pl. antitheses -·ses′ (-sēz′)

1. a contrast or opposition of thoughts, usually in two phrases, clauses, or sentences (Ex.: you are going; I am staying)
2. the second part of such an expression
3. a contrast or opposition
4. the exact opposite joy is the antithesis of sorrow

Etymology: ME antitesis < LL antithesis < Gr < antithenai < anti-, against + tithenai, to place: see do