Cool cop more casual with us (9)
I believe the answer is:
composure
'cool' is the definition.
(thesaurus)
'cop more casual with us' is the wordplay.
'casual with' is an anagram indicator (a casual or disordered version of the letters).
'cop'+'more'='copmore'
'copmore' mixed up with 'us' makes 'COMPOSURE'.
(Other definitions for composure that I've seen before include "Self-possession" , "Calm self-control" , "Aplomb" , "Coolness" , "Calm state" .)