yellow iris vs yellow flag

yellow iris and yellow flag both are nouns.

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

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

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

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

yellow iris (noun)	yellow flag (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