caltrop vs Trapa natans

caltrop and Trapa natans both are nouns.

Word	Noun	Adjective	Verb	Adverb
caltrop	Yes	No	No	No
Trapa natans	Yes	No	No	No

As nouns, Trapa natans is a hyponym of caltrop; that is, Trapa natans is a word with a more specific, narrower meaning than caltrop:

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

Other hyponyms of caltrop include Jesuits' nut, water caltrop, ling, ling ko, Trapa bicornis.

caltrop (noun)	Trapa natans (noun)
tropical annual procumbent poisonous subshrub having fruit that splits into five spiny nutlets; serious pasture weed	a variety of water chestnut
Mediterranean annual or biennial herb having pinkish to purple flowers surrounded by spine-tipped scales; naturalized in America
a plant of the genus Trapa bearing spiny four-pronged edible nutlike fruits