Green’s Dictionary of Slang

1. (UK Und.) anyone who uses manual dexterity for theft, a category that includes both pickpockets and shoplifters.

1856		H. Mayhew Great World of London I 46: ‘Mobsmen’ or those who plunder by manual dexterity, like ‘buzzers’ who pick gentlemens’ pockets.
1859		Hotten Dict. of Modern Sl. etc. 63: mobsmen, dressy swindlers.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor IV 25: ‘Mobsmen,’ or those who plunder by manual dexterity — as the ‘light-fingered gentry.’.
1864, 1867, 1870		Hotten Sl. Dict. [as cit. 1859].
1873		Sl. Dict.
1882		Sydney Sl. Dict. (2 edn) 6: Mobsmen - Pickpockets.
1889		Clarkson & Richardson Police! 260: Nearly 200 were first-class thieves or ‘swell-mobsmen’. [Ibid.] 321: Companions in crime ... Mobsmen.
1896		A. Morrison Child of the Jago (1982) 96: Few Mobsmen were at the Bag of Nails that day.
1900		Marvel XIII: 322 Jan. 4: I’ve turned out a few good mobsmen in my time, but my present pupil [...] more than tops ’em all.
1924		S. Scott Human Side of Crook and Convict Life 15: Professional crooks ranging from the lobby thief to the expert mobsman.
1949		Monteleone Criminal Sl. (rev. edn).

2. (usu. US Und.) a gangster.

c.1930		(ref. to late 19C) N. Kimball Amer. Madam (1981) 133: A lot just stayed on till they got a dose, were beaten up or killed, or went wrong with some mobsman and ended up in jail.
1938		Smith’s Wkly (Sydney) 26 Feb. 3/4: The moment was ripe for the mobsman with an organising brain.
1931		M. Harris ‘Facing the Mob’ in Gangland Stories Feb. 🌐 Jimmy was a mobsman and I’m his moll.
1935		Centralia (WA) Chronicle Advertiser 15 Nov. 4/3: Every chief mobsman has his clown.
1943		Smith & Carnes American Guerrilla 12: Well, it couldn’t be much longer before we’d be rolling up and down the narrow streets of Bengasi, somewhat like Chicago mobsmen in the old days—guns a-blazing!