Theatrical cast sit in choir (10)
I believe the answer is:
histrionic
'theatrical' is the definition.
('histrionic' can be similar in meaning to 'theatrical')
'cast sit in choir' is the wordplay.
'cast' is an anagram indicator.
'sit'+'in'+'choir'='sitinchoir'
'sitinchoir' with letters rearranged gives 'HISTRIONIC'.
(Other definitions for histrionic that I've seen before include "Overly theatrical" , "Melodramatic" , "Of acting; dramatic" .)