holy cow

holy cow Word Origin interjection Slang.

1. (used to express bewilderment, surprise, or astonishment.)

Origin of holy cow First recorded in 1920–25 Idioms and Phrases with holy cow holy cow

Also, holy mackerel or Moses or moly or smoke. An exclamation of surprise, astonishment, delight, or dismay, as in Holy cow, I forgot the wine, or Holy mackerel, you won! or Holy Moses, here comes the teacher! or Holy smoke, I didn’t know you were here too. The oldest of these slangy expletives uses mackerel, dating from about 1800; the one with Moses dates from about 1850 and cow from about 1920. None has any literal significance, and moly is a neologism devised to rhyme with “holy” and possibly a euphemism for “Moses.”