Tin perhaps contains new nuts (6)
I believe the answer is:
mental
'nuts' is the definition.
(thesaurus)
'tin perhaps contains new' is the wordplay.
'tin perhaps' becomes 'metal' (tin is a kind of metal).
'contains' means one lot of letters goes inside another.
'new' becomes 'n'.
'metal' enclosing 'n' is 'MENTAL'.
(Other definitions for mental that I've seen before include "Light allowing vehicles to turn while ahead is red" , "Cerebral" , "Barking" , "Cognitive" , "Crazy" .)