Some massive idiot (3)
I believe the answer is:
ass
'idiot' is the definition.
(I've seen this before)
'some massive' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ASS' can be found hidden inside 'massive'.
(Other definitions for ass that I've seen before include "An American backside" , "One in Bible spoke" , "Donkey - fool" , "Animal related to horses" , "Quadruped; fool" .)