a psalm: a sacred song, especially a composition from Israel's book of Psalms or one sung in that same tradition
This word began its life in ordinary Greek as the twang of a plucked string, the sound of fingers on a lyre or harp. By the time of the New Testament that musical origin had faded into the background, and the word had become the standard name for a sacred song. The Greek translators of the Old Testament had settled it on the Hebrew Psalms, titling that book with this very word, so a first-century reader heard in it above all the songbook of Israel.
The New Testament uses it in two closely related ways, and they share one core: a psalm is a sacred, sung composition tied to the world of the Psalter. Luke uses it as the plain name of the Old Testament book, or of a numbered piece within it, the way we might say "the second psalm." Paul uses it for a song actually offered up in the gatherings of the early church, one voice among the varied music of worship.
The overlap is real, and so is the difference. In Luke it points to a fixed text of Scripture. In Paul it points to a living act of singing, which may draw on the old Psalms or may be freshly composed. The English word "psalm" fits both, but it leans so hard toward the written book that it can hide the sung, sometimes new, songs Paul has in mind.
Nuances
Disputed
In Ephesians 5:19 and Colossians 3:16, whether ψαλμός, ὕμνος, and ᾠδή denote three distinct genres of song or function as near-synonyms accumulated for comprehensiveness.
- majorityThe three terms are largely interchangeable, echoing the LXX psalm-title practice where they alternate freely; Paul is characterizing the whole rich vocal life of the church rather than legislating three categories.; Andrew T. Lincoln, Ephesians, WBC 42 (Word, 1990), 346; Frank Thielman, Ephesians, BECNT (Baker, 2010), 361; Douglas J. Moo, The Letters to the Colossians and to Philemon, PNTC (Eerdmans, 2008), 289-290; David G. Detwiler, "Church Music and Colossians 3:16," Bibliotheca Sacra 158 (2001): 347-369
- minorityThe terms carry meaningful distinctions, with ψαλμός retaining a link to the Old Testament Psalter (and, on the strongest form of the view, some resonance of stringed accompaniment), ὕμνος denoting praise addressed to God, and ᾠδή the more general song.; Clinton E. Arnold, Ephesians, ZECNT (Zondervan, 2010), 353-354; Harold W. Hoehner, Ephesians: An Exegetical Commentary (Baker, 2002), 708-710; R. C. Trench, Synonyms of the New Testament, sec. 78