Stage horse (5)
I believe the answer is:
mount
This clue is a double definition.
'stage' is the first definition.
(I've seen this before)
'horse' is the second definition.
(I know that mount is a type of horse)
(Other definitions for mount that I've seen before include "hill" , "Climb - eg Everest" , "Clamber on" , "Get on - horse" , "Ascend; horse" .)