The Collaborative International Dictionary of English v.0.48:

Encyclopedist \En*cy`clo*pe"dist\, n. [Cf. F.
   encyclop['e]diste.]
   The compiler of an encyclopedia, or one who assists in such
   compilation; also, one whose knowledge embraces the whole
   range of the sciences.
   [1913 Webster]

   The Encyclopedists, the writers of the great French
      encyclopedia which appeared in 1751-1772. The editors were
      Diderot and D'Alembert. Among the contributors were
      Voltaire and Rousseau.
      [1913 Webster]

WordNet (r) 3.0 (2006):

encyclopedist
    n 1: a person who compiles information for encyclopedias [syn:
         encyclopedist, encyclopaedist]