Atheism has been mischaracterized, misbranded by the powerful noise of current secular atheists for what classical atheism is: without god, not seared unbelief.
that ye were at that time separate from Christ, alienated from the commonwealth of Israel, and strangers from the covenants of the promise, having no hope and without God [ATHEISTS] in the world. Ephesians 2:12 ASV.B
The New Testament uses the Greek word 'apistia' to characterize 'unbelief' and 'apistos' to refer to the unbelieving or the unbeliever. Hence, from the point of view of the New Testament, the correct English word to refer to the nonbeliever is 'apistist', to keep with the words theist and atheist.
Unbelief in a god is, thus, apistheist.