senior vs doyen

senior and doyen both are nouns.

Word	Noun	Adjective	Verb	Adverb
senior	Yes	Yes	No	No
doyen	Yes	No	No	No

As nouns, doyen is a hyponym of senior; that is, doyen is a word with a more specific, narrower meaning than senior:

Other hyponyms of senior include dean, doyenne, senpai.

senior (noun)	doyen (noun)
an undergraduate student during the year preceding graduation	a man who is the senior member of a group
a person who is older than you are

senior (adjective)	doyen (adjective)
older; higher in rank; longer in length of tenure or service
used of the fourth and final year in United States high school or college
advanced in years; (`aged' is pronounced as two syllables)