‘Holy cow!‘ is an exclamation of surprise used mostly in the United States, Canada, Australia and England. It is a minced oath or euphemism for ‘Holy Christ!’ Similar expressions such as ‘Holy buckets’ and ‘Holy underwear’ employ a play-on-words, ‘holy’ implying ‘riddled with holes.’
According to the ‘Dictionary of American Slang’ (1960): ‘It is also the common oath and popular exclamation put into the mouths of teenagers by many screenwriters, and, is universally heard on radio, television, and in the movies. It was first popularized by the ‘Corliss Archer’ series of short stories, television programs, and movies, which attempted to show the humorous, homey side of teenage life.’
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The Daily Omnivore 