Iris cristata vs fleur-de-lis

Iris cristata and fleur-de-lis both are nouns.

Word	Noun	Adjective	Verb	Adverb
Iris cristata	Yes	No	No	No
fleur-de-lis	Yes	No	No	No

As nouns, fleur-de-lis is a hypernym of Iris cristata; that is, fleur-de-lis is a word with a broader meaning than Iris cristata:

Iris cristata: low-growing summer-flowering iris of northeastern United States
fleur-de-lis: plants with sword-shaped leaves and erect stalks bearing bright-colored flowers composed of three petals and three drooping sepals

Other hypernyms of Iris cristata include flag, iris, sword lily.

Iris cristata (noun)	fleur-de-lis (noun)
low-growing summer-flowering iris of northeastern United States	(heraldry) charge consisting of a conventionalized representation of an iris
	plants with sword-shaped leaves and erect stalks bearing bright-colored flowers composed of three petals and three drooping sepals