Monster due to transform into monster (10)
I believe the answer is:
tremendous
'monster' is the definition.
(thesaurus)
'monster due to transform' is the wordplay.
'to transform' indicates anagramming the letters.
'monster'+'due'='monsterdue'
'monsterdue' with letters rearranged gives 'TREMENDOUS'.
'into' acts as a link.
(Other definitions for tremendous that I've seen before include "Wonderful" , "Immense" , "Fantastic" , "Terrific" , "Excellent; very great" .)