water chestnut vs water chestnut plant

water chestnut and water chestnut plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
water chestnut	Yes	No	No	No
water chestnut plant	Yes	No	No	No

As nouns, water chestnut and water chestnut plant are synonyms defined as:

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

Other synonyms of water chestnut include caltrop.

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