From Middle Dutch psalter m. Likely not directly inherited from Old Dutch psaltare n, psaltere in this form, as the expected form (in accordance with Middle Dutch L-vocalization) is souter, an obsolete form which does appear to be inherited; see there for more. Ultimately from Latin psalterium, from Ancient Greek ψᾰλτήρῐον (psăltḗrĭon). Doublet of souter, psalterie, and psalterium.