Carry out horse? (5)
I believe the answer is:
mount
I believe this is a double definition.
'carry out' is the first definition.
'horse?' is the second definition.
(mount is a kind of horse)
(Other definitions for mount that I've seen before include "Climb, stairs say" , "- - Sinai" , "seat" , "stage" , "Ascend; horse" .)