contrast has 5 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 opposition or dissimilarity of things that are compared
“in contrast to”
the act of distinguishing by comparing differences
a conceptual separation or distinction
“there is a narrow line between sanity and insanity”
the perceptual effect of the juxtaposition of very different colors
the range of optical density and tone on a photographic negative or print (or the extent to which adjacent areas on a television screen differ in brightness)
put in opposition to show or emphasize differences
“The middle school teacher contrasted her best student's work with that of her weakest student”
to show differences when compared; be different
“the students contrast considerably in their artistic abilities”
Synonyms, antonyms and the broader and narrower relations for contrast come from Princeton University’s WordNet. Full sources and licences.