Hornet ruined royal seat (6)
I believe the answer is:
throne
'royal seat' is the definition.
(I've seen this in another clue)
'hornet ruined' is the wordplay.
'ruined' is an anagram indicator.
'hornet' anagrammed gives 'THRONE'.
(Other definitions for throne that I've seen before include "Chair of state" , "toilet" , "Seat of royalty" , "Oh rent out this seat" , "Ceremonial chair for bishop or king" .)