Volunteer assassin? (5)
I believe the answer is:
offer
This clue is a double definition.
'volunteer' is the first definition.
(I know that volunteer can be written as offer)
'assassin?' is the second definition.
(someone who 'offs' people)
(Other definitions for offer that I've seen before include "Proposal; reduced price" , "Come up with" , "Provide; reduced price" , "Suggest" , "Attempt" .)