wash has 20 distinct synonyms spread across 12 of its 21 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.
move by or as if by water
“The swollen river washed away the footbridge”
be capable of being washed
“Does this material wash?”
admit to testing or proof
“This silly excuse won't wash in traffic court”
form by erosion
“The river washed a ravine into the mountainside”
to cleanse (itself or another animal) by licking
“The cat washes several times a day”
a thin coat of water-base paint
the work of cleansing (usually with soap and water)
Synonyms, antonyms and the broader and narrower relations for wash come from Princeton University’s WordNet. Full sources and licences.
the erosive process of washing away soil or gravel by water (as from a roadway)
“from the house they watched the washout of their newly seeded lawn by the water”
the flow of air that is driven backwards by an aircraft propeller
a watercolor made by applying a series of monochrome washes one over the other
garments or white goods that can be cleaned by laundering
any enterprise in which losses and gains cancel out
“at the end of the year the accounting department showed that it was a wash”