Boyd’s Bible Dictionary:

(play a stringed instrument). In Hebrew, “Praises.” The collection of one hundred and fifty lyrics which compose the nineteenth O. T. book. The liturgical hymnbook of the Hebrews, and accepted by early Christians. Authorship of seventy of them ascribed to David. The most perfect specimens of Hebrew poetry extant.

Concise Bible Dictionary:

This word occurs in the Old Testament only in connection with the Psalms of David and those in the Book of Psalms. David is called “the sweet psalmist of Israel” (2 Sam. 23:1). There can be no doubt that in connection with the “singers,” and the praising God with instruments, the Psalms were used. We read “sing psalms unto him,” “Make a joyful noise unto him with psalms,” &c. In New Testament days, for a time at least, the Psalms of David may have been sung by believers, but there were also hymns and spiritual songs, and it is to be remarked that in the singing at the institution of the Lord’s supper a hymn (ὑμνέω) is spoken of, not a psalm (φαλμός). See PASSOVER. The latter Greek word (besides the occurrences which refer to the Book of Psalms) is found in 1 Corinthians 14:26; Ephesians 5:19 and Colossians 3:16.