IPA: /ˈraɪdə/
KK: /ˈraɪdər/
A person who rides, especially on a horse or a bicycle.
The rider skillfully guided the horse through the obstacle course.
Rider → The word is formed from "ride" (from Old English *ridan*, meaning to sit on and control the movement of an animal) and "-er" (meaning a person who). A rider is a person who rides, typically on a horse or other vehicle.
Think of someone who 'controls' the movement of an animal ('ride') — that's why a rider is a person who rides.