Kate and Bill are people with intelligence (6)
I believe the answer is:
mossad
'intelligence' is the definition.
(I know that Mossad is a type of international intelligence agency)
'kate and bill are people' is the wordplay.
I cannot really understand how this works, but
'bill' could be 'ad' (advertisement stuck on wall) and 'ad' is found in the answer.
The remaining letters 'moss' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'with' is the link.
Can you help me to learn more?
(Other definitions for mossad that I've seen before include "Israeli intelligence organisation" , "Israeli intelligence service" , "Agents" , "Israeli intelligence agency" , "Israeli secret service" .)