Bug in weed (6)
I believe the answer is:
nettle
I believe this is a double definition.
'bug' is the first definition.
(thesaurus)
'weed' is the second definition.
(nettle is a kind of weed)
'in' acts as a link.
(Other definitions for nettle that I've seen before include "Stinging weed - pester" , "Sting or annoy with the plant" , "Annoy; common weed" , "Grasp it firmly and it will not sting" , "Bug" .)