Disturbed stare seen in flash master (7)
I believe the answer is:
maestro
'master' is the definition.
('maestro' can be a synonym of 'master')
'disturbed stare seen in flash' is the wordplay.
'disturbed' indicates anagramming the letters.
'seen in' indicates putting letters inside.
'flash' becomes 'mo' (I've seen this in other clues).
'stare' with letters rearranged gives 'aestr'.
'aestr' placed into 'mo' is 'MAESTRO'.
(Other definitions for maestro that I've seen before include "Famous conductor" , "hotshot" , "Genius possibly" , "Are most in favour of a foreign master?" , "Distinguished composer, conductor or performer" .)