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 

How does the New Testament speak of unbelief in its Greek? Apistia, apistos.

Those who claim unbelief in Yehoshua (Jesus), the God of Judaism do not even understand Judaism and its concept of theism and atheism.

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.

Atheism (biblical) is biblical. Exodus 20:1-6, Isaiah 45:21
Psalms 14:1 sees those who say that there is no God as foolish
The adherents of secular atheism claim that etymologically they do not believe in any gods nor in the existence of gods. Believers are usually afraid of atheists for whatever reason but in reality, the First Atheist is God (Jesus).

Psalms 14:1 ASV
(1)  For the Chief Musician. A Psalm of David. The fool hath said in his heart, There is no God. They are corrupt, they have done abominable works; There is none that doeth good.

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 

Exo 20:3-5
(3)  Thou shalt have no other gods before me [ATHEISM]. (4)  Thou shalt not make unto thee a graven image, nor any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth: (5)  thou shalt not bow down thyself unto them, nor serve them; for I Jehovah thy God am a jealous God, visiting the iniquity of the fathers upon the children, upon the third and upon the fourth generation of them that hate me,