ounce has 5 distinct synonyms spread across 3 of its 3 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 unit of apothecary weight equal to 480 grains or one twelfth of a troy pound
a unit of weight equal to one sixteenth of a pound or 16 drams or 28.349 grams
large feline of upland central Asia having long thick whitish fur
Synonyms, antonyms and the broader and narrower relations for ounce come from Princeton University’s WordNet. Full sources and licences.