Definition of "plesiomorphic"
adjective
comparative more plesiomorphic, superlative most plesiomorphic
(cladistics) Sharing a character state with an ancestral clade; primitive.
Quotations
[T]he cockroach Polyphaga may represent a condition more plesiomorphic than in other Dictyoptera, but it could as well be paedomorphic, and therefore more derived than in other Dictyoptera .
2000, Christine A. Nalepa, Claudio Bandi, “Paedomorphosis and Termite Evolution”, in Termites: Evolution, Sociality, Symbioses, Ecology, page 68