noun, plural in·fi·del·i·ties.
- marital disloyalty; adultery.
- unfaithfulness; disloyalty.
- lack of religious faith, especially Christian faith.
- a breach of trust or a disloyal act; transgression.
noun plural -ties
- lack of faith or constancy, esp sexual faithfulness
- lack of religious faith; disbelief
- an act or instance of disloyalty
c.1400, “want of faith, unbelief in religion; false belief, paganism;” also (early 15c.) “unfaithfulness or disloyalty to a person” (originally to a sovereign, by 16c. to a lover or spouse), from French infidélité, from Latin infidelitatem (nominative infidelitas) “unfaithfulness, faithlessness,” noun of quality from infidelis (see infidel).