Green’s Dictionary of Slang

(Aus.) the head.

1890		Dead Bird (Sydney) 29 Nov. 6/3: [H]ow they applauded when Purge got it hot / On the nadget or bingie or sneezer .
1899		Truth (Sydney) 30 Apr. 5/3: [headline] Virago Fallick and Her State-Child Victim —Banged and Beaten—Pot-Sticks and Walking-canes Smashed over Her Young Head [...] Smashing the Pie Dish over Mattie’s ‘Nadget’— A Sweet Specimen of the ‘Gentle Sex’!
1903		Nepean Times 26 Dec. 4/1: ’E looks at the noo eap, scratches is nadget a bit, aud then says o didn’t think they looked too well where I’d just puttem.
1911		Sun. Times (Perth) 12 Feb. 3/1: ‘If I ’it you on the nadget you’ll wake up quick an’ lively’.
1920		Sydney Sportsman (Surry hills, NSW) 2 June 7/3: Bishop led his terrible right at the nadget. Tingle bent a wee, and let it shoot over.
1925		Lachlander & Condoblin Recorder (NSW) 23 Dec. 4/7: The boys [...] have got it into their ‘nadgets’ that there is great fun to be derived from [...] entering, the female dressing shed, whilst the girls are bathing, and hiding various articles of their underwear.
1932		S. Coast Times (NSW) 18 Mar. 5/1: He turned around, and a right copped him on the back of the nadget and he sprawled to the canvas.