senior vs doer

senior and doer both are nouns.

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

As nouns, doer is a hypernym of senior; that is, doer is a word with a broader meaning than senior:

Other hypernyms of senior include actor, worker.

senior (noun)	doer (noun)
an undergraduate student during the year preceding graduation	a person who acts and gets things done
a person who is older than you are

senior (adjective)	doer (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)