Green’s Dictionary of Slang

unk n.

uncle.

1907		‘Hugh McHugh’ Beat It 99: After all the excitement was over and Unk Greg was sleeping.
1915		C.J. Dennis ‘Uncle Jim’ in Songs of a Sentimental Bloke 93: ‘I ain’t no grammarist meself, per’aps, / But langwidge is a ’elp, I owns,’ sez Unk, / ‘When things is goin’ crook.’ An’ ’ere ’e wunk.
1922		M.E. Smith Adventures of a Boomer Op. 59: This ‘Boomin’ around don’t pay, Hi [...] and your Unk Bill is going to cut it cold.
1962		(con. 1950s) H. Simmons Man Walking On Eggshells 187: Naw, Unk, you’re saying something.
2007		N. McCall Them (2008) 13: Where you been the last few days, Unk, bangin some honey on the sly?