Foul peers cavorting still (9)
I believe the answer is:
reposeful
'still' is the definition.
(I've seen this before)
'foul peers cavorting' is the wordplay.
'cavorting' is an anagram indicator.
'foul'+'peers'='foulpeers'
'foulpeers' anagrammed gives 'REPOSEFUL'.
(Other definitions for reposeful that I've seen before include "with calming effect" , "still" , "serenity" , "Laid-back" .)