tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans - Punic faith - the perfidious Judas - the fiercest and most treacherous of foes - treacherous intrigues • Syn: perfidious, treacherous • Similar to: unfaithful • Derivationally related forms: treachery (for: treacherous), perfidy (for: perfidious), perfidiousness (for: perfidious)