Source : Webster's Revised Unabridged Dictionary (1913)

Psalmist \Psalm"ist\, n. [L. psalmista, Gr. ?: cf. F. psalmiste.
   See {Psalm}.]
   1. A writer or composer of sacred songs; -- a title
      particularly applied to David and the other authors of the
      Scriptural psalms.

   2. (R. C. Ch.) A clerk, precentor, singer, or leader of
      music, in the church.

Source : WordNet®

psalmist
     n : a composer of sacred songs; "David is called The Psalmist
         because he is believed to be the author of the Book of
         Psalms"