- not faithful; false to duty, obligation, or promises; faithless; disloyal.
- not sexually faithful to a spouse or lover.
- not accurate or complete; inexact: an unfaithful translation.
- Obsolete. unbelieving; infidel.
- not true to a promise, vow, etc
- not true to a wife, husband, lover, etc, esp in having sexual intercourse with someone else
- inaccurate; inexact; unreliable; untrustworthyunfaithful copy
- obsolete not having religious faith; infidel
- obsolete not upright; dishonest
adj.mid-14c., “acting falsely,” from un- (1) “not” + faithful. In Middle English it also had a sense of “infidel, unbelieving, irreligious” (late 14c.). Sense of “not faithful in marriage” is attested from 1828. Related: Unfaithfully; unfaithfulness.