seaweed

noun

1. (uncountable, usually)Any of numerous marine algae, such as a kelp.

   “We have lingered in the chambers of the sea / By sea-girls wreathed with seaweed red and brown / Till human voices wake us, and we drown.”

   “The tide was out, and we drew up amid the strong bracing smell of seaweed, with gulls screeching, wheeling around, and gliding on the wind.”

   “There has been some investigation into the potential of seaweeds as a carbon store, and although more is needed, one study says that seaweed habitats are believed to be the most productive of all coastal vegetated ecosystems, and suggested that the world’s seaweed sequesters as much carbon as all the planet’s seagrass meadows, saltmarshes and mangroves combined.”

2. (broadly, uncountable, usually)Any of various fresh water plants and algae.

   “With light penetrating to the lake bottom, beds of seaweed flourished where little had grown before.”