cow lily vs water lily

cow lily and water lily both are nouns.

Word	Noun	Adjective	Verb	Adverb
cow lily	Yes	No	No	No
water lily	Yes	No	No	No

As nouns, water lily is a hypernym of cow lily; that is, water lily is a word with a broader meaning than cow lily:

cow lily: common water lily of eastern and central North America, having broad leaves and globe-shaped yellow flowers; in sluggish fresh or slightly brackish water
water lily: an aquatic plant of the family Nymphaeaceae

cow lily (noun)	water lily (noun)
common water lily of eastern and central North America, having broad leaves and globe-shaped yellow flowers; in sluggish fresh or slightly brackish water	an aquatic plant of the family Nymphaeaceae