Onion-Butt Share definition Flag An Onion-Butt is ther perfect ass on a woman or man. The word Onion-Butt has said to make the grown man cry because it is so beautiful. Damn, that girl got an Onion-Butt!!! Onion-Butt by Steve Y October 19, 2005 0 0 Get merch Get the Onion-Butt mug. Buy Now — $32.95 See more merch