Guide a bullock (5)
I believe the answer is:
steer
This clue is a double definition.
'guide' is the first definition.
(I know that guide can be written as steer)
'a bullock' is the second definition.
(I know that bullock can be written as steer)
(Other definitions for steer that I've seen before include "cow!" , "piece of advice" , "Direct; young ox" , "Direct, fix course" , "Con" .)