phenomenal Share definition Flag Something absolutely fantastic and one of a kind in greatness. Tends to be used to describe Irn Bru. "That's Coke's aye raj ya wee midden. Geez us an Irn Bru. It's pure phenomenal, like." phenomenal by Limbo Murfbiscuit December 1, 2004 0 0 Get merch Get the phenomenal mug. Buy Now — $32.95 See more merch