Boyd’s Bible Dictionary:
(Praise ye Jehovah). Written thus in Rev. 19:1; but HALLELUJAH, in margin of (Psa. 106; 111; 112; 113; 117; 118; 135 and so forth). A common exclamation of joy and praise in Jewish worship.
Concise Bible Dictionary:
The word ἀλληλούϊα occurs in the LXX, answering to the Hebrew word halal in the Psalms translated “praise ye the Lord.” It is an ascription of praise to God. In Revelation 19:1, 3, 4, 6 the praise is heard in heaven: through mercy the saint learns to raise his Hallelujah on his way thither.
Jackson’s Dictionary of Scripture Proper Names:
Greek for praise ye Jah Al’Ion, an oak