Source : Webster's Revised Unabridged Dictionary (1913)

Positivist \Pos"i*tiv*ist\, n.
   A believer in positivism. -- a. Relating to positivism.

Source : WordNet®

positivist
     adj : of or relating to positivism; "positivist thinkers";
           "positivist doctrine"; "positive philosophy" [syn: {positivistic},
            {positive}]

positivist
     n : someone who emphasizes observable facts and excludes
         metaphysical speculation about origins or ultimate causes
         [syn: {rationalist}]