grass widow vs woman

grass widow and woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
grass widow	Yes	No	No	No
woman	Yes	No	No	No

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

Other hypernyms of grass widow include adult female.

grass widow (noun)	woman (noun)
a divorced woman or a woman who is separated from her husband	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