tontine has 1 distinct synonym spread across 1 of its 2 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 form of life insurance whereby on the death or default of a participant his share is distributed to the remaining members
an annuity scheme wherein participants share certain benefits and on the death of any participant his benefits are redistributed among the remaining participants; can run for a fixed period of time or until the death of all but one participant
Synonyms, antonyms and the broader and narrower relations for tontine come from Princeton University’s WordNet. Full sources and licences.