Stage for a horse (5)
I believe the answer is:
mount
I believe this 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)
'for a' acts as a link.
(Other definitions for mount that I've seen before include "St. Helens, for example" , "Ascend; horse" , "Steed" , "Fix onto a backing" , "Horse; climb" .)