water cabbage vs water plant

water cabbage and water plant both are nouns.

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

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

water cabbage: pantropical floating plant forming a rosette of wedge-shaped leaves; a widespread weed in rivers and lakes
water plant: a plant that grows partly or wholly in water whether rooted in the mud, as a lotus, or floating without anchorage, as the water hyacinth

Other hypernyms of water cabbage include aquatic plant, hydrophyte, hydrophytic plant.

water cabbage (noun)	water plant (noun)
pantropical floating plant forming a rosette of wedge-shaped leaves; a widespread weed in rivers and lakes	a plant that grows partly or wholly in water whether rooted in the mud, as a lotus, or floating without anchorage, as the water hyacinth