Move in explosive missile (7)
I believe the answer is:
trident
'missile' is the definition.
(I've seen this before)
'move in explosive' is the wordplay.
'move' becomes 'ride' (ride is a kind of move**).
'in' is an insertion indicator.
'explosive' becomes 'tnt' (TNT is an example).
'ride' put inside 'tnt' is 'TRIDENT'.
(Other definitions for trident that I've seen before include "Nuclear weapon" , "Neptune's spear - missile" , "Spear with three prongs" , "Neptune's or Britannia's spear" , "Neptune's weapon" .)