synapomorphy
noun
syn·ap·o·mor·phy (ˌ)si-ˈna-pə-ˌmȯr-fē 
plural synapomorphies
: a character or trait that is shared by two or more taxonomic groups and is derived through evolution from a common ancestral form
Word History
Etymology
International Scientific Vocabulary syn- + apomorphy derived evolutionary trait or feature (from apo- + -morphy)
First Known Use
1965, in the meaning defined above