Motor inside explosive missile (7)
I believe the answer is:
trident
'missile' is the definition.
(I've seen this before)
'motor inside explosive' is the wordplay.
'motor' becomes 'ride' (both can refer to a car).
'inside' is an insertion indicator.
'explosive' becomes 'tnt' (TNT is an example).
'ride' inserted inside 'tnt' is 'TRIDENT'.
(Other definitions for trident that I've seen before include "Red tint (anag.)" , "3-pronged spear" , "Nuclear weapon" , "Submarine-launched ballistic missile" , "Nuclear missile" .)