noun
1.
a. : a tassel grass ( Ruppia maritima )
b. : a plant of the genus Salicornia (especially S. europaea )
c. : thrift 6
d. or sea hay : eelgrass 1 ; also : its dried stems widely used for stuffing furniture and in making coarse fabrics
2. : any of several seaweeds ; especially : a green alga (genus Enteromorpha ) that often causes fouling of the bottoms of ships
3. : a cirrus cloud of wavy hairlike elements