Trapa natans vs water chestnut

Trapa natans and water chestnut both are nouns.

Word	Noun	Adjective	Verb	Adverb
Trapa natans	Yes	No	No	No
water chestnut	Yes	No	No	No

As nouns, water chestnut is a hypernym of Trapa natans; that is, water chestnut is a word with a broader meaning than Trapa natans:

Trapa natans: a variety of water chestnut
water chestnut: a plant of the genus Trapa bearing spiny four-pronged edible nutlike fruits

Other hypernyms of Trapa natans include caltrop, water chestnut plant.

Trapa natans (noun)	water chestnut (noun)
a variety of water chestnut	edible bulbous tuber of a Chinese marsh plant
	Chinese sedge yielding edible bulb-shaped tubers
	a plant of the genus Trapa bearing spiny four-pronged edible nutlike fruits