Idioms and Phrases with my god
Also, my goodness. Expressions of shock, surprise, or dismay, as in My God, don't tell me he's dying, or My goodness, what an awful outfit. The first term dates from about 1800; goodness in the variant is a euphemism for God.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.