hammer has 8 distinct synonyms spread across 6 of its 10 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 hand tool with a heavy rigid head and a handle; used to deliver an impulsive force by striking
a heavy metal sphere attached to a flexible wire; used in the hammer throw
a striker that is covered in felt and that causes the piano strings to vibrate
beat with or as if with a hammer
“hammer the metal flat”
Synonyms, antonyms and the broader and narrower relations for hammer come from Princeton University’s WordNet. Full sources and licences.