WordNet records no synonym and no antonym for avulsion. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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.
an abrupt change in the course of a stream that forms the boundary between two parcels of land resulting in the loss of part of the land of one landowner and a consequent increase in the land of another
a forcible tearing or surgical separation of one body part from another
Synonyms, antonyms and the broader and narrower relations for avulsion come from Princeton University’s WordNet. Full sources and licences.