How does the Buddha define "atheist"? As usually atheist is mean a belief that there is no god. Is there any definition by Buddha about atheist ? I read philosophy that inhumanity would called atheist really other than belief in god .
Atheism falls under ucchedavāda which was vehemently rejected by the Buddha. It is one of two extremes that Buddha avoided by revealing the middle way; Pratītyasamutpāda.


  "'Everything exists': That is one extreme. 'Everything doesn't exist': That is a second extreme. Avoiding these two extremes, the Tathagata teaches the Dhamma via the middle:.."
  -Kaccayanagotta Sutta