Definition of "infidel"

(...) how it is that to his name who yesterday departed for the other world, we prefix so significant and infidel a word, and yet do not thus entitle him, if he but embarks for the remotest Indies of this living earth;(...)

1851 November 14, Herman Melville, chapter 7, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley

But not only have the priests tried to make the very term Atheism odious, as if it would destroy all of good and beautiful in nature, but some of the reformers, not having the moral courage to avow their own sentiments, wishing to be popular, fearing lest their reforms would be considered Infidel, (as all reforms assuredly are), shield themselves from the stigma, by joining in the tirade against Atheism, and associate it with everything that is vile, with the crime of slavery, the corrup­tions of the Church, and all the vices imaginable.

1881, Ernestine Rose, A Defence of Atheism, J.P. Mendum, page 20

The infidel writer is a greater enemy to society.

1779, Vicesimus Knox, On the Prevalence of Religious Scepticism

Some Muslims are taught that non-Muslims are infidels and are to be shunned.

2005, George W. Braswell, Islam and America: Answers to the 31 Most-asked Questions, page 33