infidelity

UK: /ˌɪnfɪˈdɛlɪti/ US: /ˌɪnfɪˈdɛlɪti/ ,(in′fi del′i tē)

Inflections of 'infidelity' (n): npl: infidelities

WordReference Random House Learner's Dictionary of American English © 2026

in•fi•del•i•ty /ˌɪnfɪˈdɛlɪti/   n., pl. -ties. 

1. unfaithfulness to one's partner in marriage;
   adultery:
   [uncountable] guilty of infidelity.
2. an act of adultery:
   [countable] could no longer overlook his infidelities.
3. disloyalty:
   [uncountable] acts of infidelity against our organization.
4. an act of disloyalty:
   [countable] some business infidelities.

See -fid-.

WordReference Random House Unabridged Dictionary of American English © 2026

in•fi•del•i•ty  (in′fi del′i tē), n., pl. -ties. 

1. marital disloyalty;
   adultery.
2. unfaithfulness;
   disloyalty.
3. Religion lack of religious faith, esp. Christian faith.
4. a breach of trust or a disloyal act;
   transgression.

• Latin infidēlitās, equivalent. to infidēli(s) unfaithful (see infidel) + -tās -ty²
• late Middle English 1375–1425

Collins Concise English Dictionary © HarperCollins Publishers::

infidelity / ˌɪnfɪˈdɛlɪtɪ/ noun ( -ties)

1. lack of faith or constancy, esp sexual faithfulness
2. lack of religious faith; disbelief
3. an act or instance of disloyalty