sheathn.[OE. schethe, AS. sc, sce, sc; akin to OS. skia, D. scheede, G. scheide, OHG. sceida, Sw. skida, Dan. skede, Icel. skeiir, 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. (Bot.) Any sheathlike covering, organ, or part.()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.()