chap has 12 distinct synonyms spread across 2 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.
a crack in a lip caused usually by cold
(usually in the plural) leather leggings without a seat; joined by a belt; often have flared outer flaps; worn over trousers by cowboys to protect their legs
crack due to dehydration
“My lips chap in this dry weather”
Synonyms, antonyms and the broader and narrower relations for chap come from Princeton University’s WordNet. Full sources and licences.