Sheath (?), n. [OE. schethe, AS.
scǣð, sceÁð,
scēð; akin to OS. skēðia, D.
scheede, G. scheide, OHG. sceida, Sw.
skida, Dan. skede, Icel. skeiðir, 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.
The dead knight's sword out of his sheath he
drew.
Spenser.
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) (Zoöl.) One of the
elytra of an insect.
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.