What's the difference between these two words other than obviously the spelling. I've seen some songs write Alleluia which sounds very similar to Hallelujah when sung.
Both spellings have come into English from the same origin but via different routes.
- "Hallelujah" is from the Hebrew via the Greek transliteration and is close to the original Hebrew
- "Alleluia" is from the Hebrew via the Latin.
Both transliterations began with the Hebrew. The original Hebrew word means to "Praise the LORD/YHWH"
Hallelujah is used 4 times in the NT, all of which are in Revelation 19:1-6 (see GotQuestions). The Greek word used is Ἁλληλουϊά, which transliterates most directly to Hallélouia or also to Hallelujah. The added H at the beginning comes from the rough breathing mark, which indicates to place an h sound at the beginning of the word and thus into transliterations. Another example is with the word for "the", which is ὁ (ho).
Quoting the Vine's expository dictionary, "'Alleluia,' without the initial 'H,' is actually a misspelling" (Vine, Unger, White, NT, 287).
Additionally, Hallelujah is used 24 times in the Old Testament, all of which are in 15 of the Psalms between Psalm 104-150 (source). (Though, GotQuestions says it is found over 50 times in OT). Here is the interlinear for Psalm 135:1, which starts with the exclamation that means "Praise Yahweh" (the interlinear makes this obvious and explicit). It looks like two connected words: hallu (praise) and Yah (Yahweh).