1. opposition; contrast.
2. the direct opposite.
3. a counter proposition.
4. an adversary.
5. Rhetoric: a) the juxtaposition of contrasting ideas, phrases, or words so as to produce an effect of balance, as in “Give me liberty or give me death.” b) the second sentence or part thus set in opposition, as “or give me death.”
5. Philosophy: Hegelian dialectic - comprising of three dialectical stages of development: a thesis, giving rise to its reaction, an antithesis, which contradicts or negates the thesis, and the tension between the two being resolved by means of a synthesis.
Etymology: Greek for “setting opposite”, from ἀντί “against” + θέσις “position”.