ligature has 2 distinct synonyms spread across 2 of its 6 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.
(music) a group of notes connected by a slur
character consisting of two or more letters combined into one
a metal band used to attach a reed to the mouthpiece of a clarinet or saxophone
thread used by surgeons to bind a vessel (as to constrict the flow of blood)
Synonyms, antonyms and the broader and narrower relations for ligature come from Princeton University’s WordNet. Full sources and licences.