Not loyal or trustworthy; breaking a promise, especially romantically; disloyal.
From 'un-' (not) + 'faithful,' which comes from Middle English 'faith' (from Old French 'fei,' Latin 'fides'). The word has been used since the 1500s to describe betrayal of trust, promises, or loyalty in any relationship.
The root 'fides' (faith/trust) appears in English words like 'bona fides' (good faith) and 'infidel' (lacking faith). So unfaithful is literally 'un-faithful'—the opposite of keeping the faith someone placed in you.
Historically weaponized against women as a control mechanism; female infidelity has been treated as a categorical moral failure while male infidelity normalized as human weakness. The gendered double standard persists in modern usage patterns and judgment.
Use 'infidelity' or 'breach of trust' for neutral reference. When discussing relationship betrayal, apply consistent moral standards regardless of gender.
["breach of trust","infidelity","disloyal"]
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