Green’s Dictionary of Slang

1. an expert.

1818		W. Perry London Guide 178: Another of the ir-reverends is a dabster at backgammon.
1820		Jack Randall’s Diary 7: Dick Welborn [...] That mighty dabster at his Pen.
1834		W.A. Caruthers Kentuckian in N.Y. I 64: I’m not much of a dabster at it, but if the stake ain’t too high, I don’t care if I take a fling or two.
1848		Bartlett Dict. Americanisms 107: dab, or dabster. One who is expert in anything; a proficient. A vulgar colloquialism in England and America.
1849		Paul Pry 22 Jan. n.p.: [S]ome mustachioed sharper, who is a dabster at dominoes, and throws dice to a marvel.
1854		N.Y. Pick (NY) 29 Apr. n.p.: He’s a dabster at fencing.
1854		Bell’s Life in Sydney 3 June 3/3: Every dirty three-up player, and dabster at high, low, Jack and the Game.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1877		J. Greenwood Dick Temple I 102: Not in the least like the performance of an amateur dabster. [...] Much more like the work of an old master for style and finish.
1891		Sporting Times 14 Feb. 1/3: The heroine of this romance / [...] / A dabster at song and dance.
1898		Binstead & Wells A Pink ’Un and a Pelican 236: Joe’s old woman was a dabster at book-keepin’.
1901		Marvel XV:377 Jan. 8: You’re a dabster at the bunking business.
1910		‘Doss Chiderdoss’ ‘Telling ’Em Something’ Sporting Times 3 Dec. 2/2: The Chancellor, knowing they’re open to ’ank, / Is a dabster at ladling it out.
1913		Sport (Adelaide) 21 June 9/4: They Say [...] That Punch M. thinks he is a dabster at toeball.
1925		(con. WWI) Fraser & Gibbons Soldier and Sailor Words 70: Dabster, A: A skilful fellow.
1959		Record Hackensack (NJ) 8 Sept. 45/2: [In] a special section of Australian slang I learned [...] that instead of being a ‘dabster’ (expert) I am only a ‘dag’ (humorous fellow) who is ‘giving a fly’ (making an attempt) at talking ‘fodder’ (nonsense) [...] I assure you that this is all ‘square dinkum’.
1963		H.E. Bates Oh! To be in England (1985) 355: She handles the piebald like a real dabster. All my kids are good with horses.
1968		R.F. Adams Western Words (2nd edn).

2. attrib. use of sense 1.

1919

Aussie (France) XI Feb. 5/1: Our Batt. owns a Babbling Brook who is a dabster cook, but has one great failing, common to most of his kind [...] – he doesn’t like shaving.

3. something excellent.

1906		Bulletin (Sydney) 22 Nov. 17/2: Occasionally one hears of a dabster (a variety of boshter) and a bontoshter, which denotes something abnormal in the boshter line.
1965		(con. 1940s) N. Hilliard Power of Joy 204: ‘Try a full toss!’ someone shouted. Bock: ‘Zat!’ ‘A dabster, Terry.’.