Pig-like monster goring tree (7)
I believe the answer is:
porcine
'pig-like' is the definition.
(porcine means like a pig)
'monster goring tree' is the wordplay.
'monster' becomes 'orc' (I've seen this before).
'goring' indicates putting letters inside (inserted letters gore their way into the word).
'tree' becomes 'pine' (pine is a kind of tree).
'orc' put within 'pine' is 'PORCINE'.
(Other definitions for porcine that I've seen before include "Of or like a pig" , "Piggish" , "Resembling a pig" , "Piglike" , "Piggy" .)