Ox; guide (5)
I believe the answer is:
steer
This clue is a double definition.
'ox' is the first definition.
(castrated ox)
'guide' is the second definition.
(I know that guide can be written as steer)
(Other definitions for steer that I've seen before include "Guide (eg, a ship)" , "The animal to direct" , "Exercise control" , "Navigate" , "Control movement" .)