Cyclist (5)
I believe the answer is:
rider
'cyclist' is the definition.
(someone riding a bike)
This is the entire clue.
(Other definitions for rider that I've seen before include "H. - Haggard, English novelist (She, etc)" , "Horseman or add-on verdict by jury" , "Horseman or addendum" , "Motorcyclist" , "One in the saddle" .)