In an instant, conservative monarch gets scornful (7)
I believe the answer is:
mocking
'scornful' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for mocking that I've seen before include "Raillery" , "Taunting" , "Scornfully teasing, ridiculing" , "Sarcastic" .)