Cause pain in a cow's tail joint (4)
I believe the answer is:
whip
'cause pain' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'cow's tail joint' is the wordplay.
'tail' says to take the final letters.
'joint' becomes 'hip' (part of body).
The final letter of 'cow' is 'w'.
'w'+'hip'='WHIP'
'in a' is the link.
Can you help me to learn more?
(Other definitions for whip that I've seen before include "Party official; punish" , "Fluffy dessert" , "Instrument of discipline" , "Beat (cream)" , "Flog - pinch" .)