caller has 5 distinct synonyms spread across 3 of its 9 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 bettor in a card game who matches the bet and calls for a show of hands
a person who announces the changes of steps during a dance
“you need a fiddler and a caller for country dancing”
someone who proclaims or summons in a loud voice
“the callers were mothers summoning their children home for dinner”
the person initiating a telephone call
“there were so many callers that he finally disconnected the telephone”
2 of the 9 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for caller.
Synonyms, antonyms and the broader and narrower relations for caller come from Princeton University’s WordNet. Full sources and licences.