[in.fi.del] n [ME infidele, fr. MF, fr. LL infidelis unbelieving, fr. L, unfaithful, fr. in- + fidelis faithful--more at fidelity] (15c) 1: one who is not a Christian or who opposes Christianity
2. a: an unbeliever with respect to a particular religion b: one who acknowledges no religious belief
3: a disbeliever in something specified or understood -- infidel adj