Differentia

·noun The formal or distinguishing part of the essence of a species; the characteristic attribute of a species; specific difference.

differentia
diffĕrentĭa, ae, f. [differo], I a difference, diversity (cf.: discrepantia, distantia, discrimen, ...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
differentia
differentia ae, f differo, a difference, diversity : honesti et decori: in principiis.— A species ...

An Elementary Latin Dictionary