old-maid's bonnet vs wild lupine

old-maid's bonnet and wild lupine both are nouns.

Word	Noun	Adjective	Verb	Adverb
old-maid's bonnet	Yes	No	No	No
wild lupine	Yes	No	No	No

As nouns, old-maid's bonnet and wild lupine are synonyms defined as:

old-maid's bonnet and wild lupine: stout perennial of eastern and central North America having palmate leaves and showy racemose blue flowers

Other synonyms of old-maid's bonnet include Indian beet, Lupinus perennis, sundial lupine.

old-maid's bonnet (noun)	wild lupine (noun)
stout perennial of eastern and central North America having palmate leaves and showy racemose blue flowers	stout perennial of eastern and central North America having palmate leaves and showy racemose blue flowers