See on the kindred word κακοπάθεια, suffering, Jam 5:10. Only here and 2Ti 2:3, 2Ti 2:9; 2Ti 4:5.
Let him sing psalms (ψαλλέτω)
The word means, primarily, to pluck or twitch. Hence of the sharp twang on a bowstring or harp-string, and so to play upon a stringed instrument. Our word psalm, derived from this, is, properly, a tune played upon a stringed instrument. The verb, however, is used in the New Testament of singing praise generally. See 1Co 14:15; Rom 15:9.