Safe place for eggs on island hill (9)
I believe the answer is:
incubator
This clue could be a double definition.
'safe place for eggs' is the first definition.
(device for incubating eggs)
'island hill' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'on' acts as a link.
(Other definitions for incubator that I've seen before include "Artificial substitute for a hen's warmth" , "Apparatus for hatching eggs" , "Support organization" , "Egg hatching apparatus" , "Egg-hatching apparatus" .)