old maid vs genus Zinnia

old maid and genus Zinnia both are nouns.

Word	Noun	Adjective	Verb	Adverb
old maid	Yes	No	No	No
genus Zinnia	Yes	No	No	No

old maid (noun)	genus Zinnia (noun)
a card game using a pack of cards from which one queen has been removed; players match cards and the player holding the unmatched queen at the end of the game is the loser (or `old maid')	genus of annual or perennial plants of tropical America having solitary heads of brightly colored flowers
an elderly unmarried woman
the loser in a game of old maid
commonly cultivated Old World woody herb having large pinkish to red flowers
any of various plants of the genus Zinnia cultivated for their variously and brightly colored flower heads