Green’s Dictionary of Slang

nunk n.

[? nincompoop n. (1)]

(UK Und.) a fool .

[UK]Swell’s Night Guide 61: cracksman:What a flat, send I may live, if he can stag chaff from square patter; why, you nunk, couldn’t you tumble to the pallary, nanty tumble to the queerums, a foggy nobbed’un?