Atheist \A"the*ist\, n. [Gr. ? without god; 'a priv. + ? god:
   cf. F. ath['e]iste.]
   1. One who disbelieves or denies the existence of a God, or
      supreme intelligent Being.

   2. A godless person. [Obs.]

   Syn: Infidel; unbeliever.
Infidel \In"fi*del\, n.
   One who does not believe in the prevailing religious faith;
   especially, one who does not believe in the divine origin and
   authority of Christianity; a Mohammedan; a heathen; a

   Syn: Infidel, Unbeliever, Freethinker, Deist,
        Atheist, Sceptic, Agnostic.
Freethinker \Free"think`er\, n.
   One who speculates or forms opinions independently of the
   authority of others; esp., in the sphere or religion, one who
   forms opinions independently of the authority of revelation
   or of the church; an unbeliever; -- a term assumed by deists
   and skeptics in the eighteenth century.

     n 1: the supernatural being conceived as the perfect and
          omnipotent and omniscient originator and ruler of the
          universe; the object of worship in monotheistic
          religions [syn: God, Supreme Being]
     2: any supernatural being worshipped as controlling some part
        of the world or some aspect of life or who is the
        personification of a force [syn: deity, divinity, immortal]
     3: a man of such superior qualities that he seems like a deity
        to other people; "he was a god among men"
     4: a material object that is worshipped as a god; "thou shalt
        not make unto thee any graven image"; "money was his god"
        [syn: idol, graven image]

     n 1: one who personifies an abstract quality
     2: representing an abstract quality or idea as a person or
        creature [syn: prosopopoeia]
     3: the act of attributing human characteristics to abstract
        ideas etc. [syn: incarnation]

     adj 1: existing only in the mind; separated from embodiment;
            "abstract words like `truth' and `justice'" [ant: concrete]
     2: not representing or imitating external reality or the
        objects of nature; "a large abstract painting" [syn: abstractionist,
         nonfigurative, nonobjective]
     3: based on specialized theory;  "a theoretical analysis" [syn:
     4: dealing with a subject in the abstract without practical
        purpose or intention; "abstract reasoning"; "abstract

Emphasis added where deemed necessary. Definitions obtained via