speaker has 8 distinct synonyms spread across 2 of its 3 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.
someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)
“the speaker at commencement”
electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance
the presiding officer of a deliberative assembly
“the leader of the majority party is the Speaker of the House of Representatives”
Synonyms, antonyms and the broader and narrower relations for speaker come from Princeton University’s WordNet. Full sources and licences.