Nettle and grass (4)
I believe the answer is:
nark
I believe this clue is a double definition.
'nettle' is the first definition.
('nark' can be a synonym of 'nettle')
'grass' is the second definition.
(I've seen this before)
'and' is the link.
(Other definitions for nark that I've seen before include "upset" , "one causing annoyance down under" , "cause irritation" , "Annoy (colloq.); informer" , "Rat" .)