alumna vs woman

alumna and woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
alumna	Yes	No	No	No
woman	Yes	No	No	No

As nouns, woman is a hypernym of alumna; that is, woman is a word with a broader meaning than alumna:

alumna: a female person who has received a degree from a school (high school or college or university)
woman: an adult female person (as opposed to a man)

Other hypernyms of alumna include alum, grad, graduate, adult female.

alumna (noun)	woman (noun)
a female person who has received a degree from a school (high school or college or university)	women as a class
	an adult female person (as opposed to a man)
	a female person who plays a significant role (wife or mistress or girlfriend) in the life of a particular man