slash has 23 distinct synonyms spread across 7 of its 9 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 or stir about violently
“The feverish patient thrashed around in his bed”
an open tract of land in a forest that is strewn with debris from logging (or fire or wind)
a punctuation mark (/) used to separate related items of information
Synonyms, antonyms and the broader and narrower relations for slash come from Princeton University’s WordNet. Full sources and licences.