class fellow vs classmate

class fellow and classmate both are nouns.

Word	Noun	Adjective	Verb	Adverb
class fellow	Yes	No	No	No
classmate	Yes	No	No	No

As nouns, class fellow and classmate are synonyms defined as:

Other synonyms of class fellow include schoolfellow, schoolmate.

class fellow (noun)	classmate (noun)
an acquaintance that you go to school with	an acquaintance that you go to school with