Green’s Dictionary of Slang

1. a tramp, a vagrant, a worthless person.

1740		R. North Examen 293: Great ladies are more apt to take Sides with talking, flattering Gossips than such a Shack as Fitzharris.
1848		Bartlett Dict. Americanisms.
c.1850		F.M. Whitcher Widow Bedott Papers (1883) 32: I don’t leve Bill Jinkins would a turned out such a miserable shack if he’d had a decent woman for a wife.
1864, 1867, 1870		Hotten Sl. Dict.
1882		W. Andrews Book of Oddities 84: [...] a notorious set of idlers [...] ready for anything except working for an honest living – easily earning the cognomen of Alfreton shacks [F&H].
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 200: shack, a vagabond. ‘Her father was a poor drunken shack away down in Bottle town’ (Thorn.).
1976		E. Dahlberg Olive of Minerva 162: Perhaps I’ve had some clandestine need of a shack like you.

2. (US campus) an egregiously hard worker and denigrated as such.

1891

Topeka Dly Capital (KS) 22 Feb. 2/4: Animate and inanimate objects, which in his day had been known as ‘grinds,’ ‘muckers,’ ‘shacks,’ ‘rushes,’ ‘cuts,’ ‘swipes,’ etc.

3. a railroad brakeman.

1895		Anaconda Standard (MT) 15 Dec. 10/1: ‘Der shacks begun to frisk der rods an’ dey frisked us all off’.
1899		J. Flynt Tramping with Tramps 397: SHACK: a brakeman.
1907		J. London Road 25: The ‘shack’ (brakeman) takes a coupling-pin and a length of bell-cord to the platform in front of the truck in which the tramp is riding.
1917		‘A-No. 1’ From Coast to Coast with Jack London 29: In the stock car adjoining the one we were hoboing, the shack found other trespassers.
1921		P. & T. Casey Gay-cat 189: I was purty near corraled betoon the engine crew runnin’ down from for’rd an’ the shacks comin’ up from the caboose.
1930		‘Dean Stiff’ Milk and Honey Route 26: A great many hobo writers are [...] full ready to tell the novice how to outwit the brakemen, or shacks.
1937		‘Boxcar Bertha’ Sister of the Road (1975) 230: There’s only one way that the shacks and the dicks will always let a hobo alone, and that is when he’s got a woman and a baby with him.
1947		L. M. Beebe Mixed Train Daily 313: The stock was valuable and a roundup was imperative, but, as the shacks and hoggers of the S.V. were unaccustomed to the saddle, a score of professional cowpokes were engaged for the task [DA].
1951		L. Brown Iron City 156: The link-and-pin claimed the lives of eight of his fellow shacks.
1970		(con. 1900s) Gaddis & Long Panzram (2002) 25: They rode the freights [...] at the the risk of being thrown off moving trains by tough shacks (brakemen).
1991		(con. 1920s) O.D. Brooks Legs 169: The hogger, tallow pot and head-end shack were sitting on a low pile of ties eating lunch.

4. (US Und.) a police officer.

1924

G. Henderson Keys to Crookdom 414: Police. [...] shack, hack.