Sit on (eggs) (8)
I believe the answer is:
incubate
'sit on eggs' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for incubate that I've seen before include "Help eggs to hatch" , "nurture" , "Sit on (eggs)" , "Brood" , "Develop under favourable conditions, bacteria say" .)