instrument has 9 distinct synonyms spread across 6 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.
a device that requires skill for proper use
(law) a document that states some contractual relationship or grants some right
the semantic role of the entity (usually inanimate) that the agent uses to perform an action or start a process
any of various devices or contrivances that can be used to produce musical tones or sounds
equip with instruments for measuring, recording, or controlling
Synonyms, antonyms and the broader and narrower relations for instrument come from Princeton University’s WordNet. Full sources and licences.