Peter and mate confused but self-restrained (9)
I believe the answer is:
temperate
'self-restrained' is the definition.
(I've seen this in another clue)
'peter and mate confused' is the wordplay.
'and' means one lot of letters go next to another.
'confused' indicates an anagram.
'peter' put after 'mate' is 'matepeter'.
'matepeter' with letters rearranged gives 'TEMPERATE'.
'but' is the link.
(Other definitions for temperate that I've seen before include "With mild climate" , "Showing moderation" , "comfortably warm?" , "Abstemious" , "It is reasonable" .)