councillor vs fellow member

councillor and fellow member both are nouns.

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

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

councillor: a member of a council
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 councillor include member.

councillor (noun)	fellow member (noun)
a member of a council	one of the persons who compose a social group (especially individuals who have joined and participate in a group organization)