Is Her Majesty after a cat spray? (8)
I believe the answer is:
atomiser
'spray?' is the definition.
('atomiser' can be a synonym of 'spray')
'is her majesty after a cat' is the wordplay.
'her majesty' becomes 'er' (Elizabeth Regina).
'after' is a charade indicator (letters next to each other).
'cat' becomes 'tom' (a tom is a male cat).
'is'+'er'='iser'
'a'+'tom'='atom'
'iser' after 'atom' is 'ATOMISER'.
(Other definitions for atomiser that I've seen before include "Device for reducing liquid to a fine spray" , "Dispenser for turning liquid into a fine spray" , "Dispenser spraying perfume as a fine mist" , "Perfume spray" , "Mister" .)