It grows painful to touch (6)
I believe the answer is:
nettle
This clue could be a double definition.
'it grows painful' is the first definition.
The definition suggests a singular noun which matches the answer.
'touch' is the second definition.
The definition and answer can be both to do with communicating as well as being verbs in their base form.
Perhaps there's a link between them I don't understand?
'to' acts as a link.
Can you help me to learn more?
(Other definitions for nettle that I've seen before include "Wild plant - annoy" , "Irritate, annoy" , "Bug" , "Stinging weed - pester" , "Grasp it firmly and it will not sting" .)