Source : Webster's Revised Unabridged Dictionary (1913)

Atheism \A"the*ism\, n. [Cf. F. ath['e]isme. See {Atheist}.]
   1. The disbelief or denial of the existence of a God, or
      supreme intelligent Being.

            Atheism is a ferocious system, that leaves nothing
            above us to excite awe, nor around us to awaken
            tenderness.                           --R. Hall.

            Atheism and pantheism are often wrongly confounded.
                                                  --Shipley.

   2. Godlessness.

Source : WordNet®

atheism
     n 1: the doctrine or belief that there is no God [syn: {godlessness}]
          [ant: {theism}]
     2: a lack of belief in the existence of God or gods