The Collaborative International Dictionary of English v.0.48:

Psaltery \Psal"ter*y\, n.; pl. Psalteries. [OE. sautrie, OF.
   psalterie, F. psalt['e]rion, L. psalterium psaltery, psalter,
   from Gr. ?, fr. ?. See Psalm, Psalter.]
   A stringed instrument of music used by the Hebrews, the form
   of which is not known.
   [1913 Webster]

         Praise the Lord with harp; sing unto him with the
         psaltery and an instrument of ten strings. --Ps.
                                                  xxxiii. 2.
   [1913 Webster]

WordNet (r) 3.0 (2006):

psaltery
    n 1: an ancient stringed instrument similar to the lyre or
         zither but having a trapezoidal sounding board under the
         strings