grass widow vs Duchess of Windsor

grass widow and Duchess of Windsor both are nouns.

Word	Noun	Adjective	Verb	Adverb
grass widow	Yes	No	No	No
Duchess of Windsor	Yes	No	No	No

grass widow (noun)	Duchess of Windsor (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