yellow flag vs yellow iris

yellow flag and yellow iris both are nouns.

Word	Noun	Adjective	Verb	Adverb
yellow flag	Yes	No	No	No
yellow iris	Yes	No	No	No

As nouns, yellow flag and yellow iris are synonyms defined as:

yellow flag and yellow iris: common yellow-flowered iris of Europe and North Africa, naturalized in United States and often cultivated

Other synonyms of yellow flag include Iris pseudacorus, yellow water flag.

yellow flag (noun)	yellow iris (noun)
common yellow-flowered iris of Europe and North Africa, naturalized in United States and often cultivated	common yellow-flowered iris of Europe and North Africa, naturalized in United States and often cultivated