rider vs pedaller

rider and pedaller both are nouns.

Word	Noun	Adjective	Verb	Adverb
rider	Yes	No	No	No
pedaller	Yes	No	No	No

As nouns, pedaller is a hyponym of rider; that is, pedaller is a word with a more specific, narrower meaning than rider:

Other hyponyms of rider include hang glider, pedaler.

rider (noun)	pedaller (noun)
a clause that is appended to a legislative bill	a person who rides a pedal-driven vehicle (as a bicycle)
a traveler who actively rides an animal (as a horse or camel)
a traveler riding in a vehicle (a boat or bus or car or plane or train etc) who is not operating it
a traveler who actively rides a vehicle (as a bicycle or motorcycle)