Green’s Dictionary of Slang

a euph. for God.

1540		D. Lyndsay Satyre of Thrie Estaits IV vii: Gar hang Dissait, and all his fallowis.
c.1597		Shakespeare Merry Wives of Windsor I iv: By gar, I vill kill the Jack priest [...] By gar, I vill myself have Anne Page.
1600		Dr. Dodypoll in Bullen III (1884) I i: Cornelia, by garr dis paltry marshan be too bolde, is too sawcie by garr. [Ibid.] III ii: Garzowne, what a pox do you stand heere for, de grand poltrone peznant, and see de Doctor be dus?
1631		H. Chettle Tragedy of Hoffman III F4: By gar my Lord, I will tell you fine knacks, for make him kicke vp his heeles, and cry wee, or be gar I be hange.
1757		Smollett Reprisal I iii: I be de captive of your eyes—by gar!
1760		Foote The Minor 35: De opera, pardonnez, by gar dat is meat for your master.
1776		Foote Trip to Calais in Works (1799) II 336: By gar, for de soft hand, it is de most hard I ever vas feel.
1785		E. Topham The Fool II ii: By Gar, she is not de fool, den!
1796		Sporting Mag. Dec. IX 137: ‘A trick! yes, by Gar,’ replied the conjurer.
1819		R. Waln Hermit in America on Visit to Phila. 111: ‘By gar, if I ad you ere, sair,’ shrieked a brother Frenchman.
1827		Hamel, Obeah Man I 333: Pray Garamighty to send him safe home.
1830		R.B. Peake Haunted Inn I i: By Gar, I have done de most work to collect de debt.
1842		S. Lover Handy Andy 49: And an iligant car / He was dhrawing – by gar!
1856		M. Griffith Autobiog. of a Female Slave 20: By gar, I’d like to see her be for tryin’ it.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn).
1878		Besant & Rice By Celia’s Arbour III 183: Do you think I’d split upon a pal? Gar!
1886		Nat. Police Gaz. (NY) 18 Dec. 2/2: Mile. Janish [says]: By gare ! Mme. Mathilde Cottrelly: Py tam! Annie Pixley: Bv gosh! Winnie Johnson: Shiver my socks1 Flora Walsh: By hoockey!
1893		F.P. Dunne in B.C. Schaaf Mr Dooley’s Chicago (1977) 55: ‘By gar,’ I says, surprised.
1905		R. Beach Pardners (1912) 167: By Gar! she’s gone.
1912		Mencken letter 26 Mar. in Bode New Mencken Letters (1977) 37: I used to be a poet myself—and not such a bad one, by gar!
1918		Tensas Gaz. (St Joseph, LA) 1 Mar. 3/1: ‘By gar!’ ejaculated Louis.
1941		‘Digg Mee’ ‘Observation Post’ in N.Y. Age 17 May 9/7: ‘Nasty’ Wynn has smashed the family car, by gar.