drachm 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 an eighth of an ounce or to 60 grains
a British imperial capacity measure (liquid or dry) equal to 60 minims or 3.5516 cubic centimeters
a unit of capacity or volume in the apothecary system equal to one eighth of a fluid ounce
Synonyms, antonyms and the broader and narrower relations for drachm come from Princeton University’s WordNet. Full sources and licences.