one on a high horse (4)
I believe the answer is:
snob
'one on a high horse' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for snob that I've seen before include "One looking down on others" , "He thinks that he is socially superior to others" , "who puts on airs" , "Crispin" , "Socialite" .)