Irritate at the plant (6)
I believe the answer is:
nettle
'irritate' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for nettle that I've seen before include "Grasp it firmly and it will not sting" , "Provoke" , "Upset" , "Annoy; common weed" , "Sting or annoy with the plant" .)