Source : Webster's Revised Unabridged Dictionary (1913)

Theorist \The"o*rist\, n. [Cf. F. th['e]oriste.]
   One who forms theories; one given to theory and speculation;
   a speculatist. --Cowper.

         The greatest theoretists have given the preference to
         such a government as that which obtains in this
         kingdom.                                 --Addison.

Source : WordNet®

theorist
     n : someone who theorizes (especially in science or art) [syn: {theoretician},
          {theorizer}, {theoriser}]