The Collaborative International Dictionary of English v.0.48:

Purist \Pur"ist\, n. [Cf. F. puriste.]
   1. One who aims at excessive purity or nicety, esp. in the
      choice of language.
      [1913 Webster]

            He [Fox] . . . purified vocabulary with a
            scrupulosity unknown to any purist.   --Macaulay.
      [1913 Webster]

   2. One who maintains that the New Testament was written in
      pure Greek. --M. Stuart.
      [1913 Webster] Puristic

WordNet (r) 3.0 (2006):

purist
    n 1: someone who insists on great precision and correctness
         (especially in the use of words)