Green’s Dictionary of Slang

1. large female breasts.

1978		Eble Campus Sl. Apr. 3: kazoom – a woman’s breast. He made a comment about the kazooms of the girl wearing the tight sweater.
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: kahoonas (ka-hooo-naaaz) n. Large wobbly breasts; golden bodangers; kermungers.
1999		Guardian Weekend 18 Sept. 76: A bloke with a ginger bouffant kept staring at my cahoonas and winking at me.
2013		R. Johns Man Drought [ebook] ‘One of them, I think the redhead with the big kahoonas—’ ’Granddad!’ ‘Sorry, breasts’.

2. (US) the testicles; thus fig., courage.

2008		S. Rincavage Another 101 Poems 11: When I think of men with big kahoonas, the one-armed river runner is at the top of my list.
2010		A.J. Through My Eyes 18: Steve not only had a great character and respected women, but he had some big kahoonas to take on three guys.
2013		J.D. Medwar H.B.’s Big Heist 2: You’re on if you still got the kahoonas homey, get ready for another beating!