Incubate (5)
I believe the answer is:
hatch
'incubate' is the definition.
(I know that incubate can be written as hatch)
This is all the clue.
(Other definitions for hatch that I've seen before include "Dream up" , "Of young bird or fish, emerge from egg" , "Think up" , "Trapdoor cover" , "Draw fine lines" .)