Easton's Bible Dictionary
Occurs only Ephesians 5:19 and Colossians 3:16. The verb to "sing an hymn" occurs Matthew 26:30 and Mark 14:26. The same Greek word is rendered to "sing praises" Acts 16:25 (R.V., "sing hymns") and Hebrews 2:12. The "hymn" which our Lord sang with his disciples at the last Supper is generally supposed to have been the latter part of the Hallel, comprehending Psalm 113-118. It was thus a name given to a number of psalms taken together and forming a devotional exercise.
The noun hymn is used only with reference to the services of the Greeks, and was distinguished from the psalm. The Greek tunes required Greek hymns. Our information regarding the hymnology of the early Christians is very limited.
Noah Webster's New International Dictionary of the English Language
1. (n.) An ode or song of praise or adoration; especially, a religious ode, a sacred lyric; a song of praise or thanksgiving intended to be used in religious service; as, the Homeric hymns; Watts' hymns.
2. (v. t.) To praise in song; to worship or extol by singing hymns; to sing.
3. (v. i.) To sing in praise or adoration.