A punitive measure (3)
I believe the answer is:
rod
'measure' is the definition.
(rod is a kind of measure)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for rod that I've seen before include "Cane - shaft" , "Stick; angler" , "Little boy" , "Sceptre" , "Former measure equal to a quarter of a chain" .)