charter member vs fellow member

charter member and fellow member both are nouns.

Word	Noun	Adjective	Verb	Adverb
charter member	Yes	No	No	No
fellow member	Yes	No	No	No

As nouns, fellow member is a hypernym of charter member; that is, fellow member is a word with a broader meaning than charter member:

charter member: one of the original members when an organization was founded
fellow member: one of the persons who compose a social group (especially individuals who have joined and participate in a group organization)

Other hypernyms of charter member include member.

charter member (noun)	fellow member (noun)
one of the original members when an organization was founded	one of the persons who compose a social group (especially individuals who have joined and participate in a group organization)