Do an etching of an overarching sky but not much detail (7)
I believe the answer is:
sketchy
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for sketchy that I've seen before include "Cursory" , "Imprecise" , "lacking detail" , "first draft" , "Deep cave; evidence of road wear" .)