The Collaborative International Dictionary of English v.0.48:

Psalter \Psal"ter\, n. [OE. psauter, sauter, OF. sautier,
   psaltier, F. psautier, from L. psalterium. See Psaltery.]
   1. The Book of Psalms; -- often applied to a book containing
      the Psalms separately printed.
      [1913 Webster]

   2. Specifically, the Book of Psalms as printed in the Book of
      Common Prayer; among the Roman Catholics, the part of the
      Breviary which contains the Psalms arranged for each day
      of the week.
      [1913 Webster]

   3. (R. C. Ch.) A rosary, consisting of a hundred and fifty
      beads, corresponding to the number of the psalms.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Psalter
    n 1: a collection of Psalms for liturgical use [syn: Psalter,
         Book of Psalms]