Mass inspiring god, Mars' device? (7)
I believe the answer is:
warhead
'mars' device?' is the definition.
(Mars is the god of war)
'mass inspiring god' is the wordplay.
'mass' becomes 'wad' (both can mean an amount of something).
'inspiring' indicates putting letters inside.
'god' becomes 'rhea' (Rhea is an example).
'wad' placed around 'rhea' is 'WARHEAD'.
(Other definitions for warhead that I've seen before include "Explosive missile part" , "bit of a weapon" , "Missile's explosive" , "Missile explosive unit" , "Explosive part of a weapon" .)