cyclist vs biker

cyclist and biker both are nouns.

Word	Noun	Adjective	Verb	Adverb
cyclist	Yes	No	No	No
biker	Yes	No	No	No

As nouns, cyclist and biker are synonyms defined as:

Other synonyms of cyclist include bicycler, bicyclist, wheeler.

cyclist (noun)	biker (noun)
a person who rides a bicycle	a person who rides a bicycle