Green’s Dictionary of Slang

1. a large marble used for shooting (typically a child’s prize marble) .

1881		Poverty Bay Herald 29 Mar. 2: Away he runs to the Post Office, draws out his stamp money, and goes in for ‘alleytores,’ ‘stoneys,’ and ‘bonsers’.
1918		[in Orsman DNZE].
1937		Auckland Star 25 May 6: The marbles or ‘allies’ were of different classes. There were ‘moobies’, ‘glassies’, ‘bonces’, ‘chalkies’, and ‘fuds’.
1972, 1989		[in Orsman DNZE].

2. a good thing; an excellent or extreme example.

1893		Observer (Auckland) 14 Oct. 20: of a racehorse] Brockleigh, notwithstanding he will have to carry a big load of 9-8 has been jumped into the position of first favourite; and allowing that he is a ‘boncer’ over the distance, he will have to be something approaching a Carbine to win.
1896		Otago Witness 30 Jan. 37: The latter is always springing musical surprises on his audiences, his ‘Railway medley’ being ‘a bonser,’ as the pittite has it.
1898		N.Z. Herald (Auckland) 30 July 1: Ain’t it a Boncer? What? The Music Box at Jubilee Bazaar, top of Pitt-street.
1901		Observer (Auckland) 28 Sept. 7: The hamper that went out to Nihotapu with the Councillors on Monday was a ‘boncer’.
1902		Molong Exp. (NSW) 1 Feb. 11/1: The Federation Protection tariff in full operation. It’s a ‘bonser’ too.
1902		Sydney Sportsman 9 Apr. 3/4: The fish are very shy, but those who understand the sport are often rewarded for their patience and perseverance by landing a ‘bonser’.
1903		Wellington Times (NSW) 17 Sept. 5/2: Look out for Foley’s advertisement next week. It’s to be a ‘bonsor’.
1904		Taranaki Herald 9 July 1: [advert] Ox and Sheep Kidneys in galore; real boncers.
1903		Cobar Herald (NSW) 26 Dec. 2/4: [A] large number of friends visited the happy couple at their residence, partaking of wine and cake (the cake must have been a boncer).
1904		Morn. Post (Cairns) 22 Sept. 5/2: Emanuel told witness that he had five ‘boncers’ in the yard, three cows and two bullocks.
1904		Bulletin (Sydney) 14 Apr. 29/1: Re that bulwark of Austral Slanguage — ‘Bonster’. .. A bonser or bonster is comparatively superior to a bons.
1908		Feilding Star 2 May 2: The mushrooms were shown to our runner boy, and he says they are ‘bonsers!’.
1910		Eve. News (Sydney) 25 Mar. 7/3: ‘Crikey, it’s a bonser!’ exclaims one small boy, as he stood [...] lost in admiration of a pumpkin bigger than himself.
1929		Auckland Star 20 Feb. 6: [of a spectacular explosion] As the crowd wasn’t paying for the damage, such expressions of, ‘Ah, a beauty!’ ‘My word, she’s a boncer!’ were heard as underwriters wrung their hands.
1930		Auckland Star 30 Apr. 6: ‘Once I grew a case of plums. Boncers, they was; corkers.’.
1937		Auckland Star 10 Aug. 6: ‘Fair cracked ’is ’ead a boncer.’.

3. an expert; an admirable person; a beautiful woman.

1897		Auckland Star supp. 3 Apr. 2: ‘Of course the hero of the meeting was A.H. Holder, and let me tell you he is a ‘boncer’ .
1899		Observer (Auckland) 7 Oct. 20: If the ‘Boncer’ did not show form worthy of a rep. in the football match played last Saturday between the fire brigade and the Tapuites?
1900		Woodville Examiner 4 July 20: Lieut. Sommerville is a fair boncer, and we think a terrible lot of him.
1902		Lithgow Mercury (NSW) 9 Dec. 4/1: W. Peacock’s destructive bowling – 6 for 9 –was the deed that did the trick, and ‘Billy’ is described as being a ‘boncer’ with the ball.
1904		Taranaki Herald 16 Jan. 2: On Saturday, the second eleven, who are better known as ‘The Otako Boncers,’ met the Warea team.
1910		Observer (Auckland) 23 Apr. 22: Dr. Hardie Neil again distinguished himself as leader, and Robertson was a boncer as scorer.