Green’s Dictionary of Slang

1. (US) an errand boy or clerk.

1813		P. Hawker Diary (1893) I 7 Jan. 66: Mr. Macintosh [...] a good fag, an old sportsman.
1827		Sporting Mag. May 12/2: Though by no means good fags, a French chasseur will be in the field before daylight .
1839		W.A. Miles Poverty, Mendicity and Crime; Report 113: No. 17, aged 16, was the fag for an older thief named Jones.
1848		Sam Sly 30 Dec. 3/2: It is not true that R—t M—e is a barrister’s fag in the Temple.
1854		Thackeray Newcomes I 171: Bob Trotter, the diminutive fag of the studio, who ran all the young men’s errands.
1859		Matsell Vocabulum.
1860		R. Nicholson Rogue’s Progress (1966) 134: [...] now and then acting fag in an attorney’s office.
1884		Dundee Courier 12 Feb. 7/6: A kind-hearted Quaker grocer [...] got him a place as a warehouse ‘fag’.
1895		Crowe Aus. Sl. Dict. 27: Fag, a lawyer’s clerk.

2. a young female fish seller [abbr. fishfag under fish n.¹ ].

1836		‘Jack of Horslydown’ in Flash Casket 59: And you top sawyer ’mongst the fags, / Shall ride about the town.
1879		London Life 2 Aug. 7/1: [She] imbibes her ‘drops’ [...] in a manner that would astonish many of the gin-drinking fags who infest the pubs.
1894		Mirror of Life 5 May 14/3: Down Billingsgate the ‘fags’ [...] loaded down with a basket of fish, will prance along in a sort of a half dance.

3. (US/Aus.) a lawyer’s clerk.

1859		Matsell Vocabulum.
1941		Baker Popular Dict. Aus. Sl.