Jack, that touchy fellow (5)
I believe the answer is:
frost
This clue could be a double definition.
'jack' is the first definition.
The definition and answer can be both to do with contact as well as being verbs in their base form.
Perhaps there's an association between them I don't understand?
'touchy fellow' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'that' is the link.
Can you help me to learn more?
(Other definitions for frost that I've seen before include "Rime" , "Robert ---, US poet" , "Chilly feeling" , "Ice forming in cold weather" , "Ice crystals forming a white deposit" .)