discourse has 9 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.
extended verbal expression in speech or writing
an address of a religious nature (usually delivered during a church service)
an extended communication (often interactive) dealing with some particular topic
“the book contains an excellent discussion of modal logic”
to consider or examine in speech or writing
“The author talks about the different aspects of this question”
talk at length and formally about a topic
“The speaker dissertated about the social politics in 18th century England”
Synonyms, antonyms and the broader and narrower relations for discourse come from Princeton University’s WordNet. Full sources and licences.