debate has 11 distinct synonyms spread across 5 of its 6 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
argue with one another
“We debated the question of abortion”
think about carefully; weigh
“They considered the possibility of a strike”
a discussion in which reasons are advanced for and against some proposition or proposal
“the argument over foreign aid goes on and on”
the formal presentation of a stated proposition and the opposition to it (usually followed by a vote)
Synonyms, antonyms and the broader and narrower relations for debate come from Princeton University’s WordNet. Full sources and licences.