Green’s Dictionary of Slang

1. (US tramp) a dirty or ill-mannered person.

[1887		M. Roberts Western Avernus (1924) 152: ‘Siwash’ [in Chinook jargon] is an Indian, and ‘sitcum siwash’ a half-breed].
1897		A.H. Lewis Wolfville 2345: ‘You can bet it ain’t no Siwash,’ says ’Doby. ‘It’s clean strain, that infant is, if I does say it.’.
1901		W. Irwin Love Sonnets of a Hoodlum XIII n.p.: Am I never Johnnie-on-the-spot When any wooden Siwash ought to be.
1907		R. Service ‘The Low-Down White’ in Songs of a Sourdough 55: Where even the squalid Siwash now holds me a black disgrace.
1915		H.L. Wilson Ruggles of Red Gap (1917) 47: Know you, why, you knock-kneed old Siwash, I could pick out your hide in a tanyard!
1919		Van Loan ‘Piute vs. Piute’ in Score by Innings (2004) 311: You a Piute? You’re a Siwash, that’s what you are! A Siwash!
1931		Irwin Amer. Tramp and Und. Sl. 170: Siwash. – An Indian of the Salishan tribe, none too clean in their habits and person, hence any unclean or uncouth individual.
1935		H.L. Davis Honey in the Horn 11: Having called the Indian boy a grass-hopper eating Siwash, and the Housekeeping girl Popeyes, he went.

2. (US) any small, archetypal college; also attrib.

1924		Dispatch (Moline, IL) 13 Aug. 9/2: Alumni and friends of Siwash University.
1935		Rhinelander Dly News (WI) 10 Jan. 6/4: Once upon a time the writer was attending dear old Siwash College. This was before his expulsion.
1941		Dwight L. Bolinger ‘Among the New Words’ in AS XVI:4 309: siwash n. A jerkwater college.
1942		P. Wylie Generation of Vipers 244: Siwash, the corny, did not vanish in the golden nineties, it overspread the educational scene; and now [...] every university is Siwash.
1947		Time 13 Jan. 59/2: His comparatively small (31 million) audience [...] includes collegians (from Harvard to Siwash) and their professors [DA].
1974		Herald (Jasper, IN) 24 Feb. 16/1: Ten students of Knox College [...] are promoting the new ‘Siwash Look’ — a clean shaved head.
1979		Maledicta III:2 162: siwash n [...] 2: Secondrate college.