button 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. Its one recorded opposite is unbutton.
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 round fastener sewn to shirts and coats etc to fit through buttonholes
an electrical switch operated by pressing
“the elevator was operated by push buttons”
any of various plant parts that resemble buttons
a round flat badge displaying information and suitable for pinning onto a garment
“they passed out campaign buttons for their candidate”
any artifact that resembles a button
Synonyms, antonyms and the broader and narrower relations for button come from Princeton University’s WordNet. Full sources and licences.