Airy fairy British adjective informal
Irrational, imaginative, and unrealistic thinking.
I'm not sure, man. That idea sounds a bit airy-fairy to me.
Helen always comes up with airy-fairy ideas that will never work.
Impossible or unrealistic dreams, hopes, or plans
To pursue unrealistic or impossible goals
Used when one dies or something is no longer useful.
To indicate something which is no longer working and helpful or someone is on the verge of death or died.
It's possible that this phrase comes from a line in the poem Lilian written by Tennyson in 1830:
“airy, fairy Lilian”
A legal matter that is very easy to solve
The house owners didn't lock the doors before going out, and that's why they got broken in. This is an open and shut case.