Equestrian (5)
'equestrian' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rider that I've seen before include "knight" , "Equestrian added by a jury?" , "One who's got up" , "One in the saddle" , "Revere, for example" .)
'equestrian' is the definition.
(I know that horseman is a type of equestrian)
This is the entire clue.
(Other definitions for horseman that I've seen before include "mounted rider" , "Equestrian" , "Male rider" , "(Skilled) rider" , "Jockey" .)
(Other definitions for eventer that I've seen before include "Competitive horse/rider" , "Competing horse or rider" , "Equestrian competitor" , "competitive horse" , "versatile horse" .)