Loathe one in HMS Pinafore Covent Garden's mounted (5)
I believe the answer is:
abhor
'loathe' is the definition.
(synonyms)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for abhor that I've seen before include "Loathe, detest" , "Regard with disgust and hatred" , "Can't bear" , "Abominate" , "cannot stand" .)