Green’s Dictionary of Slang

1. (US Und.) a criminal’s unskilled accomplice; any type of hired thug.

1859		Matsell Vocabulum 41: heeler An accomplice of the pocket-book dropper. The heeler stoops behind the victim, and strikes one of his heels as if by mistake; this draws his attention to the pocket-book that lies on the ground.
1893		J. Hawthorne Confessions of Convict 23: With the help of his heeler and aid-de-camp [...] Bray continued to work off most of his grudges.
1899		H.E. Hamblen Yarn of Bucko Mate 114: Jake was stabbed to the heart with his own dirk, an’ his heeler, Portugee Joe, says it was a Gringo sailor.
1903		A.H. Lewis Boss 127: Jimmy the Blacksmith and his heelers are driving our people from the polls.
1950		Goldin et al. DAUL 94/1: Heeler. 1. A bouncer, especially in shady establishments.

2. (US) a hanger-on who performs tasks for a politician or political party in the hope of personal aggrandizement.

1876		N.Y. Times 26 June 1/1: A gentleman happened to say that the gang in the room was composed of Tammany ‘heelers’.
1888		C.D. Warner Their Pilgrimage 268: To have fine clothes, drink champagne, and pose in a fashionable bar-room in the height of the season – is not this the apotheosis of the ‘heeler’ and the ward ‘worker’?
1895		J.S. Wood Yale Yarns 84: It’s run entirely by Dwight Hall heelers.
1903		A.B. Hart Actual Government 99: The local man, often called a ‘heeler,’ has his body of adherents [DA].
1910		H. Hapgood Types from City Streets 59: A young ‘heeler’ who claims to be ‘very near’ Tim Sullivan is one of the most charming fellows of my acquaintance.
1920		A. Baer Two & Three 12 Feb. [synd. col.] Where is the ward heeler, Abou Ben Ahmed? May his bribe increase.
1929		J. Lait Broadway Melody 8: An entrenched battalion of burglars, sheiks, corruptionists, cake eaters, flask toters and theatrical heelers to plug it — and, presto!
1933		H. Asbury Barbary Coast (2002) 79: Enlisted under Broderick’s banner were many former Tammany heelers and sluggers.
1939		Howsley Argot: Dict. of Und. Sl.
1949		Monteleone Criminal Sl. (rev. edn).
1952		Lait & Mortimer USA Confidential 68: It is usually necessary to make a special under-table payment to a union heeler who bosses the particular project.
1962		S. Longstreet Flesh Peddlers (1964) 179: G-stringed, tassel-nippled strippers for a ward heelers’ stag in Jersey City.

3. any form of servant or accomplice.

1886		Nat. Police Gaz. (NY) 22 May 14/2: The New York heelers were going to make a clean sweep with their brooms.
1894		Star-Gaz. (Elmira, NY) 15 May 4/3: Yale College Slang [...] [A]fter feeding my face I blew down to Mory’s with a couple of heelers.
1895		Mirror of Life 31 Aug. 3/2: At that time Mitchell was surrounded by his ‘heelers,’ while Corbett was practically friendless. In his attack on Fitzsimmons the circumstances were different. Corbett had his ‘heelers’ about him, while Fitz was alone.
1899		‘Pot’ & ‘Swears’ Scarlet City 40: The prelate’s heeler unearthed a copy of Bell’s Life [...] and proceeded to read the account of a prize fight.

4. (US Und.) a sneak thief.

1910		H. Hapgood Types from City Streets 56: No one except a thief has a keener sense of gratitude. A notorious heeler said to me ‘Do you know...’.
1935		A.J. Pollock Und. Speaks.
1949		Monteleone Criminal Sl. (rev. edn).