speech has 13 distinct synonyms spread across 6 of its 8 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.
the act of delivering a formal spoken communication to an audience
“he listened to an address on minor Roman poets”
(language) communication by word of mouth
“his speech was garbled”
something spoken
“he could hear them uttering merry speeches”
the exchange of spoken words
“they were perfectly comfortable together without speech”
your characteristic style or manner of expressing yourself orally
“his manner of speaking was quite abrupt”
a lengthy rebuke
“a good lecture was my father's idea of discipline”
Synonyms, antonyms and the broader and narrower relations for speech come from Princeton University’s WordNet. Full sources and licences.