\Ne`re*o*cys"tis\, n. [NL. See {Nereid}, and
{Cyst}.] (Bot.)
A genus of gigantic seaweeds.
Note: {Nereocystis Lutkeana}, of the North Pacific, has a
      stem many fathoms long, terminating in a great vesicle,
      which is crowned with a tuft of long leaves. The stem
      is used by the Alaskans for fishing lines.