Green’s Dictionary of Slang

1. a German or one of German origins .

1890–1904		Farmer & Henley Sl. and Its Analogues.
1906		C. M’Govern ‘Soldier Sl.’ in Sarjint Larry an’ Frinds n.p.: square-head:—A soldier of German birth and addicted to the use of German idioms.
1908		Sun. Times (Perth) 5 Jan. 1/1: The Dutchman employed made a holy mess [and] a cwt. of putty will be necessary to plug the work of the ‘good-iron’ square-head.
1914		Bulletin (Sydney) 22 Oct. 10/3: So the miserable enemies of Britain were again sent to the fervent patriots below. The latter immediately came on deck and informed the wide world that they were going to work with no blessed squareheads, and formally declared a strike.
1919		H.C. Witwer Smile A Minute 52: What we have did to them Germans, Joe, in the last coupla weeks has been aplenty [...] and they ain’t no race horse on earth could keep up with them squareheads they way they been runnin’.
1929		(con. 1916) F. Manning Her Privates We (1986) 208: ’E’s a bloody German spy, that’s what ’e is [...] One o’ them fuckin’ square-heads, an’ they let ’im off!
1936		(con. 1920s) Dos Passos Big Money in USA (1966) 980: That damn squarehead make the boys work so hard they can’t get a hardon when they go to bed.
1942		Western Mail (Perth) 4 June 2/2: He seems to be a cross between a squarehead and a Jap.
1949		W.R. Burnett Asphalt Jungle in Four Novels (1984) 162: It’s Riemenschneider. The Squarehead.
1959		D. Niland Big Smoke 164: ‘What is he—a squarehead or what?’ ‘I don’t know. He’s got an accent.’.
1967		K. Kolb Getting Straight 131: Even a dumb squarehead like you oughta be able to sell something today!
1995		Gazette (Montreal) 22 Jan. 4: The squareheads, who didn’t speak frog, dismissed the erudite young frog as a crackpot.
2023		M. Herron Secret Hours 232: ‘When I need a lesson in the use of appropriate language [...] ‘I’ll not be looking for it from a slack-jawed squarehead’.

2. (Aus./US) a Scandinavian.

1906		C. Fowler letter 28 June in Tomlinson Rocky Mountain Sailor (1998) 131: The Monadnock numbers among her petty officers a great many Swedes, Danes, and men of kindred nationalities—we call them ‘square heads’ or ‘ditty boxes’ .
1912		Van Loan ‘Little Sunset’ in Ten-Thousand-Dollar Arm 102: The Terrible Swede got off to a flying start [...] ‘I knew the old squarehead would be all right.’.
1920		E. O’Neill Anna Christie Act II: You’re not old Square-head’s woman.
1929		S. Ornitz Haunch Paunch and Jowl 213: I find that there is no such thing, as yet, as an American workman. They are to each other – Hunks, Wops, Squareheads, Kikes, Micks and Heinies.
1931		P.J. Wolfson Bodies are Dust (2019) [ebook] ‘He’s a Swede, a square-head and dumb’.
1936		K. Mackenzie Living Rough 23: You know that big square-head, Gumboot Olsen.
1953		T. Runyon In For Life 266: I’m going to get that Squarehead some Christmas.
1966		T.V. Olsen Hard Men (1974) 11: Soderstrom eyed her darkly [...] ‘What you think, missus, is you talking to one big dumb squarehead, eh?’.
1976		H. Selby Jr Demon (1979) 9: One neighborhood over the other; the Irish over the squareheads.
1986		J. Ellroy Silent Terror 238: ‘Lars Anderson, big dumb handsome squarehead, cabinetmaker from the Wisconsin boonies’.

3. (US) a Pole.

1935

J. Conroy World to Win 202: That son-of-a-bitchin’ squarehead! [...] You can’t trust them Polacks.

4. (Can.) an Anglophone Canadian.

1978

Maledicta II:1+2 Summer/Winter 171: Squarehead [...] In Quebec, an Anglophone.