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.
      [1913 Webster]

            The dead knight's sword out of his sheath he drew.
                                                  --Spenser.
      [1913 Webster]

   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.
          [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Primitive \Prim"i*tive\, a. [L. primitivus, fr. primus the
   first: cf. F. primitif. See Prime, a.]
   1. Of or pertaining to the beginning or origin, or to early
      times; original; primordial; primeval; first; as,
      primitive innocence; the primitive church. "Our primitive
      great sire." --Milton.
      [1913 Webster]

   2. Of or pertaining to a former time; old-fashioned;
      characterized by simplicity; as, a primitive style of
      dress.
      [1913 Webster]

   3. Original; primary; radical; not derived; as, primitive
      verb in grammar.
      [1913 Webster]

   Primitive axes of coordinate (Geom.), that system of axes
      to which the points of a magnitude are first referred,
      with reference to a second set or system, to which they
      are afterward referred.

   Primitive chord (Mus.), that chord, the lowest note of
      which is of the same literal denomination as the
      fundamental base of the harmony; -- opposed to derivative.
      --Moore (Encyc. of Music).

   Primitive circle (Spherical Projection), the circle cut
      from the sphere to be projected, by the primitive plane.


   Primitive colors (Paint.), primary colors. See under
      Color.

   Primitive Fathers (Eccl.), the acknowledged Christian
      writers who flourished before the Council of Nice, A. D.
      325. --Shipley.

   Primitive groove (Anat.), a depression or groove in the
      epiblast of the primitive streak. It is not connected with
      the medullary groove, which appears later and in front of
      it.

   Primitive plane (Spherical Projection), the plane upon
      which the projections are made, generally coinciding with
      some principal circle of the sphere, as the equator or a
      meridian.

   Primitive rocks (Geol.), primary rocks. See under
      Primary.

   Primitive sheath. (Anat.) See Neurilemma.

   Primitive streak or Primitive trace (Anat.), an opaque
      and thickened band where the mesoblast first appears in
      the vertebrate blastoderm.
      [1913 Webster]

   Syn: First; original; radical; pristine; ancient; primeval;
        antiquated; old-fashioned.
        [1913 Webster]