A gender-inverted variant of "God knows."
1. No one knows; I have no idea. Goddess knows how long it will take for my application to be processed. A: "How do you think you did on your exam?" B: "Goddess knows!"
2. It is absolutely certain or definite (that something is true or the case). Goddess knows I need to do well on this test or I can kiss my scholarship goodbye!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.