old maid flower vs zinnia

old maid flower and zinnia both are nouns.

Word	Noun	Adjective	Verb	Adverb
old maid flower	Yes	No	No	No
zinnia	Yes	No	No	No

As nouns, old maid flower and zinnia are synonyms defined as:

old maid flower and zinnia: any of various plants of the genus Zinnia cultivated for their variously and brightly colored flower heads

Other synonyms of old maid flower include old maid.

old maid flower (noun)	zinnia (noun)
any of various plants of the genus Zinnia cultivated for their variously and brightly colored flower heads	any of various plants of the genus Zinnia cultivated for their variously and brightly colored flower heads