Reagent or explosive in machine (9)
I believe the answer is:
generator
'machine' is the definition.
(generator is a kind of machine)
'reagent or explosive' is the wordplay.
'explosive' is an anagram indicator.
'reagent'+'or'='reagentor'
'reagentor' with letters rearranged gives 'GENERATOR'.
'in' acts as a link.
(Other definitions for generator that I've seen before include "Electricity producer" , "Dynamo or similar machine" , "Engine to produce electricity" , "meant to be electrifying?" , "It gives power" .)