The Greek form (Revelation 19:1,3,4,6) of the Hebrew Hallelujah = Praise ye Jehovah, which begins or ends several of the psalms (106,111,112,113, etc.).
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Alleluia'". "Easton's Bible Dictionary".