water caltrop vs caltrop

water caltrop and caltrop both are nouns.

Word	Noun	Adjective	Verb	Adverb
water caltrop	Yes	No	No	No
caltrop	Yes	No	No	No

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

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

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

water caltrop (noun)	caltrop (noun)
a variety of water chestnut	tropical annual procumbent poisonous subshrub having fruit that splits into five spiny nutlets; serious pasture weed
	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