grass wrack vs water plant

grass wrack and water plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
grass wrack	Yes	No	No	No
water plant	Yes	No	No	No

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

grass wrack: submerged marine plant with very long narrow leaves found in abundance along North Atlantic coasts
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 grass wrack include aquatic plant, hydrophyte, hydrophytic plant.

grass wrack (noun)	water plant (noun)
submerged marine plant with very long narrow leaves found in abundance along North Atlantic coasts	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