involution has 8 distinct synonyms spread across 4 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.
reduction in size of an organ or part (as in the return of the uterus to normal size after childbirth)
a long and intricate and complicated grammatical construction
marked by elaborately complex detail
the act of sharing in the activities of a group
“the teacher tried to increase his students' engagement in class activities”
the process of raising a quantity to some assigned power
Synonyms, antonyms and the broader and narrower relations for involution come from Princeton University’s WordNet. Full sources and licences.