crest has 6 distinct synonyms spread across 3 of its 7 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 top line of a hill, mountain, or wave
the top or extreme point of something (usually a mountain or hill)
“the view from the peak was magnificent”
(heraldry) in medieval times, an emblem used to decorate a helmet
reach a high point
“The river crested last night”
Synonyms, antonyms and the broader and narrower relations for crest come from Princeton University’s WordNet. Full sources and licences.