monkey has 15 distinct synonyms spread across 3 of its 4 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.
any of various long-tailed primates (excluding the prosimians)
play around with or alter or falsify, usually secretively or dishonestly
“Someone tampered with the documents on my desk”
do random, unplanned work or activities or spend time idly
“The old lady is usually mucking about in her little house”
Synonyms, antonyms and the broader and narrower relations for monkey come from Princeton University’s WordNet. Full sources and licences.