Green’s Dictionary of Slang

a mild, euph. oath; lit. ‘God’s truth!’; thus ’strewth! excl.

1866		Argosy July 123: Gawdstruth†, aint he a bubblyjock! [...] † This adjuration is [...] employed by the poor with no more idea of the meaning than they would of the meaning of ’zounds.
1866		J. Greenwood Night in a Workhouse 16: Why, a cove forgot his toke! Gordstruth! you wouldn’t ketch me a-forgettin’ mine.
1904		Living Age CCXL 809/1: ‘Gawdstruth,’ he moaned, ‘I be wholly killed.’.
1905		A. Binstead Mop Fair 138: Gawdstroth, Bill, I’ve run half over Brighton to find yer!
1906		Sun. Times (Perth) 9 Sept. 4/8: To be hoped that his favorite push terms, such as ‘dicken,’ ‘boshter,’ ‘shicker,’ ‘gordstruth,’ and ‘fair dinkum’ were tabooed by the chairman.
1909		Sun. Times (Perth) 15 Aug. 4s/8: Oh Gorstruth! [...] Monty’s but a coot.
1910		Bulletin (Sydney) 1 Dec. 18/1: Shut up, you blokes! Bert’s on a good thing now! / Gorstrooth, you are a lot of flamin’ cows! / Do ’ave a bit o’ common! Shut yer row!
1919		Strand LVII 127/1: ‘Gawdstruth! What is it now?’ muttered Mrs. Huggins.
1919		C.H. Thorp Handful of Ausseys 3/1: Gordstruth! That cheque was to have took me to the Melbourne Cup.
1924		C.J. Dennis ‘The Knight’s Return’ in Chisholm (1951) 85: Gawstruth, I do! It ain’t so much the fack / That I ’ave soiled me soul be breakin’ trust.
1936		Western Champion (Qld) 12 Dec. 3/1: Gorstruth!
1928		J.H. Turner When the Gods Grinned 170: ‘Gawdstruth!’ he said, and his protruding eyeballs ranged from one end of the scene to the other.
1937		R. Westerby Wide Boys Never Work (1938) 112: Gawdstrewth!
1937		E. Flynn Beam Ends 72: Gawdstruth, there’s not a pound o’ guts among the lot of yer.
1939		Western Mail (Perth) 19 Jan. 11/1: ‘Gorstrewth’ was the startled, delighted exclamation.
1947		(con. late 19C) F. Clune Ben Hall the Bushranger 78: ‘Gawdstruth!’ exclaimed Gardiner. ‘Just look at that now.’.
1955		Atlantian (US Penitentiary, Atlanta, GA) 5: Gawdstruth, I’d never ’ave left London if I’d remembered this abominable climate.
1961		D. Hewett Bobbin Up 154: ‘Gawd struth,’ Nell exploded. ‘Doncha know there’s no food to waste in this house.’.
1965		E. O’Connor Irishman 125: Gawdstruth, she’s bad because — How old are you, son?
1981		J. Sullivan ‘Big Brother’ Only Fools and Horses [TV script] God struth.
1990		E. Gaitens Dance of the Apprentices 241: Gawdstruth! Mean ter sy yer don’t know wot a vanload is?
2005		(con. WWII) G. Hutchinson Eyewitness 83: Gawd struth, Corp., one thing you’ve always got plenty of round ’ere – and that’s blasted barbed wire.