Green’s Dictionary of Slang

1. (UK tramp/US, also dorne) a coin.

1844		in Spirit of the Times (N.Y.) 21 Sept. 349: In town with a pocketful of dornicks.
1905		Bluefield Daily Tel. (WV) 11 Mar. 4/2: In addition [...] the following [names for money] are given: [...] Dornes.
1907		Wash. Times (DC) 15 Dec. 46/7: ‘Dornicks,’ ‘seeds,’ ‘rocks’ [...] all referring [...] to the national currency.
1912		Leamington Spa Courier 20 Sept. 7/1: There are a great many tramps staying in this district at the present time [...] In addition to ‘gagging’ ‘scran’ (food) and ‘thonicks’ (coppers), they also get hold of a lot of old ‘clobber’ (clothes).

2. (also darnick) a stone or (half) brick, as used for violence.

1857		Louisville Dly Courier (KY) 29 Jan. 3/2: He broke in his door, and threatened him with a big rock [...] a dornick that would have required an Ajax to upheave.
1901		Sydney Sportsman (Surry Hills, NSW) 6 Feb. 2/7: Other folks that ain’t as capable as he is heave dornicks at him an’ call him a monster o’ greed.
1927		F.M. Thrasher Gang 180: Edmond Werner, fifteen, self-styled leader of the roving Northwest Side gang which carries the cognomen of the ‘Belmonts’—and pockets of darnicks.
1933		Butler & Driscoll Dock Walloper 2: clews to the butler vernacular [...] dornick—half a brick, Irish confetti.

3. a precious stone, a piece of jewellery.

1944

J. Archibald ‘Skip Tracer Bullets’ in Popular Detective June 🌐 Once he had risked his life preventing a hold-up in the jewelry store downtown. A rough person had grabbed some dazzling dornicks.