tribesman vs fellow member

tribesman and fellow member both are nouns.

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

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

tribesman: someone who lives in a tribe
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 tribesman include member.

tribesman (noun)	fellow member (noun)
someone who lives in a tribe	one of the persons who compose a social group (especially individuals who have joined and participate in a group organization)