noun unfaithfulness to the marriage vow or contract; violation of the marriage covenant by adultery.
2. infidelity ·noun breach of trust; unfaithfulness to a charge, or to moral obligation; treachery; deceit; as, the infidelity of a servant.
3. infidelity ·noun want of faith or belief in some religious system; especially, a want of faith in, or disbelief of, the inspiration of the scriptures, of the divine origin of christianity.