sea grass

1a :  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