ETYM Old Eng. psalm, salm, AS. sealm, Latin psalmus, psalma, from Greek, to pull, twitch, to play upon a stringed instrument, to sing to the harp: cf. Old Fren. psalme, salme, French psaume.
Any sacred song used to praise the Deity.

One of the 150 lyrical poems and prayers that comprise the Book of Psalms in the Old Testament; said to have been written by David.
Sacred poem or song of praise. The Book of Psalms in the Old Testament is divided into five books containing 150 psalms, traditionally ascribed to David, the second king of Israel. In the Christian church they may be sung antiphonally in plainsong or set by individual composers to music in a great variety of styles, from Josquin Desprez’s De profundis to Igor Stravinsky’s Symphony of Psalms 1930.