Weapon involving unusual risk (4)
I believe the answer is:
kris
'weapon' is the definition.
(I've seen this before)
'unusual risk' is the wordplay.
'unusual' indicates anagramming the letters.
'risk' is an anagram of 'KRIS'.
'involving' is the link.
(Other definitions for kris that I've seen before include "Its flag has a maple leaf" , "Malaysian knife with a scalloped edge" , "Malay knife" , "Malayan dagger" , "Wavy-edged dagger" .)