Someone guilty of infidelity is cheating on a spouse or romantic partner. A common cause of divorce and heartbreak is infidelity.

Fidel means "faithful" or "loyal." Tack on the prefix in, which means "not," and you've got yourself infidelity — the act of being unfaithful. The word can also be used to refer to someone's religious beliefs. Run angrily through a church and claim that God doesn't exist, and your fellow churchgoers will think you lack faith, or that you are guilty of infidelity.

Definitions of infidelity
  1. noun
    the quality of being unfaithful
    synonyms: unfaithfulness
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    faithfulness, fidelity
    the quality of being faithful
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    faithlessness, falseness, fickleness, inconstancy
    unfaithfulness by virtue of being unreliable or treacherous
    the quality of being disloyal
    disloyalty to the government or to established authority
    subversiveness, traitorousness, treason
    disloyalty by virtue of subversive behavior
    perfidiousness, perfidy, treachery
    betrayal of a trust
    type of:
    an essential and distinguishing attribute of something or someone
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