hydrate has no recorded synonym. 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. Its one recorded opposite is dehydrate.
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.
supply water or liquid to in order to maintain a healthy balance
“the bicyclists must be hydrated frequently”
become hydrated and combine with water
cause to be hydrated; add water or moisture to
“hydrate your skin”
Synonyms, antonyms and the broader and narrower relations for hydrate come from Princeton University’s WordNet. Full sources and licences.
any compound that contains water of crystallization