Queen in combat scare (6)
I believe the answer is:
fright
'scare' is the definition.
('fright' can be a synonym of 'scare')
'queen in combat' is the wordplay.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'in' means one lot of letters goes inside another.
'combat' becomes 'fight' ('fight' can be a synonym of 'combat').
'r' placed within 'fight' is 'FRIGHT'.
(Other definitions for fright that I've seen before include "Grotesque" , "A scare or shock" , "Sudden feeling of fear" , "Sudden exposure to fear" , "Terror" .)