Rotarian vs fellow member

Rotarian and fellow member both are nouns.

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

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

Rotarian: a member of a Rotary Club
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 Rotarian include member.

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