Peer admitted being naughty is deliberate (12)
I believe the answer is:
premeditated
'is deliberate' is the definition.
('premeditated' can be similar in meaning to 'deliberate')
'peer admitted being naughty' is the wordplay.
'being naughty' indicates an anagram.
'peer'+'admitted'='peeradmitted'
'peeradmitted' with letters rearranged gives 'PREMEDITATED'.
(Other definitions for premeditated that I've seen before include "Planned in advance" , "Thought out beforehand" , "Planned beforehand" , "Considered" .)