Green’s Dictionary of Slang

1. (orig. US) a gangster.

1917		Lincoln Eve. News (NE) 11 July 4: Many mobsters have left the city, it is asserted, and leaders of the mob are going to be hard to find .
1930		J. Lait Gangster Girl 151: Cyclone Tim’s order crackled like a rookery fire through the district; in groups and singly his mobsters crawled from their dark holes.
1933		‘Goat’ Laven Rough Stuff 24: Some of the best mobs around the Loop were playing billiards and pool.
1947		I. Shulman Amboy Dukes 4: Speaking reverently to real mobsters who might pass by.
1954		J. Thompson Swell-Looking Babe 18: He had been the brains [...] of a group of black-market mobsters.
1961		J.A. Williams Night Song (1962) 40: The mobbers caught his father shortchanging on hooch.
1969		M. Puzo Godfather 366: He’s not a crazy machine-gunning mobster.
1972		P. Fordham Inside the Und. 31: The mobster [...] has to have a substantial clientele to live.
1988		R. McGough An Imaginary Menagerie 59: Ever see a lobster dine with a mobster? / The Crayfish Twins did.
1999		Indep. Rev. 10 June 3: Police are constantly asking mobsters [...] to ‘rat on’ their friends.
2002		50 Cent ‘Wanksta’ 🎵 Me I’m no mobsta / Me I’m no gangsta / Me I’m no hitman, me I’m just me, me.

2. a member of the US Mafia.

1985		N. Pileggi Wiseguy (2001) 185: A top mobster, who was a member of the Joe Colombo crime family.
1999		Guardian G2 12 July 17: A mobster who takes Prozac and visits a shrink?
2000		Guardian Editor 7 Jan. 13: The mobsters have been yielding their turf to the Latinos.

3. (N.Z. prison) a member of the biker and prison gang the Mongrel Mob.

1991		B. Payne Staunch 27: [The Stormtroopers] were once allowed to come to a Mongrel Mob convention but it made me sick! The Mobsters who permitted it [...] found the error of their ways later.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 118/1: mobster n. a member of the Mongrel Mob gang.