Green’s Dictionary of Slang

iah n.

[proper name Jah, i.e. Jehovah, Rastafarian use for God + Rastafarian pfx i- to imply the spirituality that encompasses all humans, thus obviating the need for individual personal pronouns]

(W.I.) a term of address to a friend.

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[WI]Francis-Jackson Official Dancehall Dict. 26: Iah friend; term of comradeship: u. wha’ a gwaan, iah.