Infidel is defined literally as "one without faith" and is today technically an archaic term referring to anyone who doubts or denies the tenets of whichever religion is most popular in a society. According to this definition, an infidel in one society may be a True Believer in a neighboring society. Being an infidel is thus always technically relative to whatever religion possesses the most social, cultural, and political power at any given time.
According to the Oxford English Dictionary, the definition of infidel is:
1. One who does not believe in (what the speaker holds to be) the true religion; an 'unbeliever'.
2. In specific applications: a. From a Christian point of view: An adherent of a religion opposed to Christianity; esp. a Muhammadan, a Saracen (the earliest sense in Eng.); also (more rarely), applied to a Jew, or a pagan. Now chiefly Hist.
2.b From a non-Christian (esp. Jewish or Muhammadan) point of view: = Gentile, Giaour, etc.
3. A disbeliever in religion or divine revelation generally; especially one in a Christian land who professedly rejects or denies the divine origin and authority of Christianity; a professed unbeliever. Usually a term of opprobrium.
B.1 Of persons: Unbelieving; adhering to a false religion; pagan, heathen, etc. (Cf. the n.)
In practice, the label infidel today tends to be applied to freethinkers and critical atheists. During the modern era some atheists adopted the definition of infidel for their own use and to describe the fact that not only do they not believe in any gods, but also that they question, doubt, and challenge the tenets of popular religion. Such atheists reject the negative implications of the definition of infidel and instead argue that it should be treated as a positive label.
Every atheist is an infidel; so is not every infidel an atheist.
- Jackson Creed, 1625
There are many Infidels, and vnbeleeuers in the world who haue no faith at all.
- Prynne Anti-Armin., 1630
I love to consider an Infidel, whether distinguished by the Title of Deist, Atheist, or Free-thinker.
- Steele Tatler, 1709
He not only peremptorily affirms the reality of witches, but he says that those who deny their existence are not merely infidels but atheists.
- Buckle Civiliz., 1857