quadruple has 7 distinct synonyms spread across 3 of its 5 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 set of four similar things considered as a unit
a quantity that is four times as great as another
having four units or components
“quadruple rhythm has four beats per measure”
increase fourfold
“His stock earning quadrupled”
Synonyms, antonyms and the broader and narrower relations for quadruple come from Princeton University’s WordNet. Full sources and licences.