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.

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) (Zo["o]l.) 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.

Source: Webster's Revised Unabridged Dictionary (1913)