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.
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).