The Collaborative International Dictionary of English v.0.48:

Lasso \Lass"o\ (l[a^]s"s[-o]) n.; pl. Lassos (-s[=o]z). [Sp.
   lazo, L. laqueus. See Lace.]
   A rope or long thong of leather with a running noose, used
   for catching horses, cattle, etc.
   [1913 Webster]

   Lasso cell (Zool.), one of a peculiar kind of defensive and
      offensive stinging cells, found in great numbers in all
      c[oe]lenterates, and in a few animals of other groups.
      They are most highly developed in the tentacles of
      jellyfishes, hydroids, and Actini[ae]. Each of these cells
      is filled with, fluid, and contains a long, slender, often
      barbed, hollow thread coiled up within it. When the cell
      contracts the thread is quickly ejected, being at the same
      time turned inside out. The thread is able to penetrate
      the flesh of various small, soft-bodied animals, and
      carries a subtle poison by which they are speedily
      paralyzed and killed. The threads, at the same time, hold
      the prey in position, attached to the tentacles. Some of
      the jellyfishes, as the Portuguese man-of-war, and
      Cyanea, are able to penetrate the human skin, and
      inflict painful stings in the same way. Called also
      nettling cell, cnida, cnidocell.
      [1913 Webster]