Weapon involving risk (4)
I believe the answer is:
kris
'weapon' is the definition.
(I've seen this before)
'involving risk' is the wordplay.
'involving' indicates anagramming the letters.
'risk' is an anagram of 'KRIS'.
(Other definitions for kris that I've seen before include "Malay dagger - for Kristofferson?" , "Wavy-edged dagger" , "weapon" , "Malayan slashing knife" , "Indonesian dagger; sounds like fold" .)