A lot vs. Alot: 9 Grammatical Pitfalls
also halleluiah, 1530s, from Hebrew hallalu-yah "praise ye Jehovah," from hallalu, plural imperative of hallel "to praise" also "song of praise," from hillel "he praised," of imitative origin, with primary sense being "to trill." Second element is yah, shortened form of Yahweh, name of God. Replaced variant formation alleluia (12c.).
praise ye Jehovah, frequently rendered "Praise ye the LORD," stands at the beginning of ten of the psalms (106, 111-113, 135, 146-150), hence called "hallelujah psalms." From its frequent occurrence it grew into a formula of praise. The Greek form of the word (alleluia) is found in Rev. 19:1, 3, 4, 6.