meeting has 7 distinct synonyms spread across 6 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.
a small informal social gathering
“there was an informal meeting in my living room”
a casual or unexpected convergence
“he still remembers their meeting in Paris”
the social act of assembling for some common purpose
“his meeting with the salesmen was the high point of his day”
the act of joining together as one
“the merging of the two groups occurred quickly”
a place where things merge or flow together (especially rivers)
“Pittsburgh is located at the confluence of the Allegheny and Monongahela rivers”
Synonyms, antonyms and the broader and narrower relations for meeting come from Princeton University’s WordNet. Full sources and licences.