n. & adj.
--n.
1. a person who does not believe in religion or in a particular religion; an unbeliever.
2 hist. an adherent of a religion other than Christianity, esp. a Muslim.
--adj.
1. that is an infidel.
2 of unbelievers.
Etymology: ME f. F infid{egrave}le or L infidelis (as IN-(1), fidelis faithful)