Jewish, from Hebrew "Jehovah/Yahweh is my God"; OT, 1 & 2 Kings.

Whilst not much in evidence in the UK, Elijah was used by early Puritan settlers in the US and, more recently, has found favour amongst Black Muslims.

Eliyahu is the Hebrew version of the name.

ONC gives the derivation of Elliot from a Norman surname, itself derived from an Old French male name Elie. This is in turn derived from an Old French form of Elias, the Greek for Elijah.