Emily Dickinson Lexicon

IN-FI-DEL'I-TY, n. [Fr. infidelité; L. infidelitas.]

1. In general, want of faith or belief; a withholding of credit.
2. Disbelief of the inspiration of the Scriptures, or the divine original of Christianity; unbelief. There is no doubt that vanity is one principal cause of infidelity. – Knox.
3. Unfaithfulness, particularly in married persons; a violation of the marriage covenant by adultery or lewdness.
4. Breach of trust; treachery; deceit; as, the infidelity of a friend or a servant. In this sense unfaithfulness is most used.