a. [ L. infidelis; pref. in- not + fidelis faithful, fr. fides faith: cf. F. infidèle. See Fidelity. ] Not holding the faith; -- applied by Christians to one who does not believe in the inspiration of the Scriptures, and the supernatural origin of Christianity; used by Muslims to refer to those who do not believe in Islam. [ 1913 Webster +PJC ]

The infidel writer is a great enemy to society. V. Knox. [ 1913 Webster ]

n. One who does not believe in the prevailing religious faith; a heathen; a freethinker; -- used especially by Christians and Muslims. [ 1913 Webster +PJC ]

☞ Infidel is used by English writers to translate the equivalent word used Muslims in speaking of Christians and other disbelievers in Muslimism.

Syn. -- Infidel, Unbeliever, Freethinker, Deist, Atheist, Sceptic, Agnostic. An infidel, in common usage, is one who denies Christianity and the truth of the Scriptures. Some have endeavored to widen the sense of infidel so as to embrace atheism and every form of unbelief; but this use does not generally prevail. A freethinker is now only another name for an infidel. An unbeliever is not necessarily a disbeliever or infidel, because he may still be inquiring after evidence to satisfy his mind; the word, however, is more commonly used in the extreme sense. A deist believes in one God and a divine providence, but rejects revelation. An atheist denies the being of God. A sceptic is one whose faith in the credibility of evidence is weakened or destroyed, so that religion, to the same extent, has no practical hold on his mind. An agnostic remains in a state of suspended judgment, neither affirming nor denying the existence of a personal Deity. [ 1913 Webster ]

n.; pl. Infidelities [ L. infidelitas: cf. F. infidélité. ] [ 1913 Webster ]

1. Lack of faith or belief in some religious system; especially, a lack of faith in, or disbelief of, the inspiration of the Scriptures, of the divine origin of Christianity. [ 1913 Webster ]

There is, indeed, no doubt but that vanity is one of the principal causes of infidelity. V. Knox. [ 1913 Webster ]

2. Unfaithfulness to the marriage vow or contract; violation of the marriage covenant by adultery. [ 1913 Webster ]

3. Breach of trust; unfaithfulness to a charge, or to moral obligation; treachery; deceit; as, the infidelity of a servant. “The infidelity of friends.” Sir W. Temple. [ 1913 Webster ]