The Collaborative International Dictionary of English v.0.48:

Sheath \Sheath\, n. [OE. schethe, AS. sc[=ae][eth],
   sce['a][eth], sc[=e][eth]; akin to OS. sk[=e][eth]ia, D.
   scheede, G. scheide, OHG. sceida, Sw. skida, Dan. skede,
   Icel. skei[eth]ir, pl., and to E. shed, v.t., originally
   meaning, to separate, to part. See Shed.]
   1. A case for the reception of a sword, hunting knife, or
      other long and slender instrument; a scabbard.
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            The dead knight's sword out of his sheath he drew.
                                                  --Spenser.
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   2. Any sheathlike covering, organ, or part. Specifically:
      (a) (Bot.) The base of a leaf when sheathing or investing
          a stem or branch, as in grasses.
      (b) (Zool.) One of the elytra of an insect.
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   Medullary sheath. (Anat.) See under Medullary.

   Primitive sheath. (Anat.) See Neurilemma.

   Sheath knife, a knife with a fixed blade, carried in a
      sheath.

   Sheath of Schwann. (Anat.) See Schwann's sheath.
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