grass widow vs Mrs. Simpson

grass widow and Mrs. Simpson both are nouns.

Word	Noun	Adjective	Verb	Adverb
grass widow	Yes	No	No	No
Mrs. Simpson	Yes	No	No	No

grass widow (noun)	Mrs. Simpson (noun)
a divorced woman or a woman who is separated from her husband	United States divorcee whose marriage to Edward VIII created a constitutional crisis leading to his abdication