Calm queen seen running round (6)
I believe the answer is:
'calm' is the definition.
(I know that calm can be written as serene)
'queen seen running round' is the wordplay.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'running' indicates an anagram.
'round' indicates putting letters inside.
'seen' is an anagram of 'sene'.
'er' placed into 'sene' is 'SERENE'.
(Other definitions for serene that I've seen before include "without any trouble" , "Not agitated" , "Impassive" , "Calm and at peace" , "Calm and unclouded" .)