Just plastic is tougher (9)
I believe the answer is:
righteous
'just' is the definition.
(similar in meaning)
'plastic is tougher' is the wordplay.
'plastic' indicates an anagram (plastic can mean easily moulded).
'is'+'tougher'='istougher'
'istougher' is an anagram of 'RIGHTEOUS'.
(Other definitions for righteous that I've seen before include "Morally justified" , "law-abiding" , "Just, upright" , "Good!" , "Moral - virtuous" .)