Kernel of an idea (4)
I believe the answer is:
germ
'kernel of an idea' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for germ that I've seen before include "Disease-causing microorganism" , "Small organism that spreads disease" , "Cause of some diseases" , "Tiny organism that spreads disease" , "Bug" .)