UNFA'ITHFULNESS, noun Neglect or violation of vows, promises, allegiance or other duty; breach of confidence or trust reposed; perfidiousness; treachery; as the unfaithfulness of a subject to his prince or the state; the unfaithfulness of a husband to his wife, or of a wife to her husband; the unfaithfulness of an agent, servant or officer.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI