Weapon that's fine to change after end of week (5)
I believe the answer is:
knife
'weapon' is the definition.
(knife is a kind of weapon)
'fine to change after end of week' is the wordplay.
'to change' is an anagram indicator.
'after' means one lot of letters go next to another.
'end of' says to take the final letters.
The final letter of 'week' is 'k'.
'fine' is an anagram of 'nife'.
'nife' put after 'k' is 'KNIFE'.
'that's' is the link.
(Other definitions for knife that I've seen before include "Attack" , "Potential weapon" , "Cutting instrument" , "Use this to carve" , "Carver" .)