PERFID'IOUS, adjective [Latin perfidus; per and fidus, faithful. Per in this word signifies through, beyond, or by, aside.] 1. Violating good faith or vows; false to trust or confidence reposed; treacherous; as a perfidious agent; a perfidious friend. [See Perfidy.] 2. Proceeding from treachery, or consisting in breach of faith; as a perfidious act. 3. Guilty of violated allegiance; as a perfidious citizen; a man perfidious to his country.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI