custom has 7 distinct synonyms spread across 4 of its 5 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.
accepted or habitual practice
Synonyms, antonyms and the broader and narrower relations for custom come from Princeton University’s WordNet. Full sources and licences.
a specific practice of long standing
habitual patronage
“I have given this tailor my custom for many years”
made according to the specifications of an individual