A justifiable punch (5)
I believe the answer is:
right
This clue is a double definition.
'a justifiable' is the first definition.
(thesaurus)
'punch' is the second definition.
(I've seen this before)
(Other definitions for right that I've seen before include "''The customer is always .....''" , "The hand to the east when facing north" , "Most favourable" , "Conservative - correct" , "one side" .)