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. 23:11Now these be the last words of David. David the son of Jesse said, and the man who was raised up on high, the anointed of the God of Jacob, and the sweet psalmist of Israel, said, (2 Samuel 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 14:2626How is it then, brethren? when ye come together, every one of you hath a psalm, hath a doctrine, hath a tongue, hath a revelation, hath an interpretation. Let all things be done unto edifying. (1 Corinthians 14:26); Ephesians 5:1919Speaking to yourselves in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord; (Ephesians 5:19) and Colossians 3:1616Let the word of Christ dwell in you richly in all wisdom; teaching and admonishing one another in psalms and hymns and spiritual songs, singing with grace in your hearts to the Lord. (Colossians 3:16).