misnomer (n.)

mid-15c., in law, "an error in a name, mistaken identification of an accused or convicted person," from Anglo-French, Old French mesnomer "to misname, wrongly name," noun use of infinitive, from mes- "wrongly" (see mis- (2)) + nomer "to name," from Latin nominare "nominate" (see nominate). For noun use of French infinitives, see waiver. Meaning "act of applying a wrong name or designation" is from 1630s.