God/goodness/Heaven knows

God knows

1. No one knows (except for God). God knows how long it will take for my application to be processed. A: "How do you think you did on your exam?" B: "God knows!"
2. It is absolutely true, certain, or definite that; it is obvious or clear that. God knows I need to do well on this test or I can kiss my scholarship goodbye!
See also: god, know

goodness knows

1. No one knows. (A variant of "God knows.") Goodness knows how long it will take for my application to be processed. A: "How do you think you did on your exam?" B: "Goodness knows!"
2. It is true, certain, or definite that; it is obvious or clear that. Goodness knows I need to do well on this test, or I can kiss my scholarship goodbye!
See also: goodness, know

heaven knows

1. No one knows (except for God or the heavens). Heaven knows how long it will take for my application to be processed. A: "How do you think you did on your exam?" B: "Heaven knows!"
2. It is absolutely true, certain, or definite that; it is obvious or clear that. Heaven knows I need to do well on this test or I can kiss my scholarship goodbye!
See also: heaven, know
Farlex Dictionary of Idioms.

God knows

Also, goodness knows; heaven knows.
1. Truly, certainly, definitely, as in God knows I need a winter coat. This expression, which originated about 1300 as God wot, does not necessarily imply that God is all-knowing but merely emphasizes the truth of the statement it accompanies. The variants using goodness and heaven are euphemisms that avoid taking God's name in vain. [Second half of 1500s]
2. Also, God only knows. Only God knows, that is, neither I nor anyone else knows, as in God knows where I've stored those photos, or God only knows how many people will join the march. [Second half of 1500s]
See also: god, know
The American Heritage® Dictionary of Idioms by Christine Ammer.

God/goodness/Heaven knows

(spoken)
1 I do not know; no one knows: ‘What’s going to happen next?’ ‘God knows.’
2 used for adding emphasis to a statement, opinion, etc: God knows how he manages to survive on such a small salary. I’m no gardening expert, goodness knows!(Some people may find the use of God knows offensive.)
See also: god, goodness, heaven, know
Farlex Partner Idioms Dictionary
See also:
  • God knows
  • God knows (that) I've tried
  • God only knows
  • God only knows!
  • wot
  • (the) gods only know
  • find God
  • by God
  • T.G.I.F.
  • TGIF