slate has 2 distinct synonyms spread across 2 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.
(formerly) a writing tablet made of slate
a fine-grained metamorphic rock that can be split into thin layers
designate or schedule
“He slated his talk for 9 AM”
enter on a list or slate for an election
“He was slated for borough president”
Synonyms, antonyms and the broader and narrower relations for slate come from Princeton University’s WordNet. Full sources and licences.