British slang, interjection, exclamation of surprise short for "God's truth".
From Monty Python's Flying Circus Episode 1: Whither Canada?

Mozart: Thank you, Eddie. And now time for this week's request death. (taking card off piano) For Mr and Mrs Violet Stebbings of 23 Wolverston Road, Hull, the death of Mr Bruce Foster of Guildford.
Cut to a lounge setting. Mr Foster sitting in chair.
Foster: Strewth! (he dies)
by gorgo September 11, 2006
An Australian, or "Aussie", exclaimation, similar to the somewhat more popular "Crikey!"
Strewth, that was a hard day, toss me a Fosters mate!
by Avatar May 27, 2003
Cockney East End abreviation of "It's the truth".
"Strewth Guv would I lie to you?
by Linda Massey October 22, 2007
An Australian, or "Aussie", slang term, similar to the somewhat more popular "Crikey!"
Strewth, why is it that everybody thinks we Aussies drink Fosters. I wouldn't even feed that to my dog.
by Cock-juggling-thunder-cunt November 24, 2012
An Australianism or Aussieism for "bloody hell" or "Geeze" or "holy cow", is usually an expression of surprise or disgust or amazement.
G'day mate, strewth you had us all bloody scared when we saw you with that bush pig in the car.
by Woohzal March 11, 2008