primitive sheath

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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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.
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   2. Of or pertaining to a former time; old-fashioned;
      characterized by simplicity; as, a primitive style of
      dress.
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   3. Original; primary; radical; not derived; as, primitive
      verb in grammar.
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   {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.
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   Syn: First; original; radical; pristine; ancient; primeval;
        antiquated; old-fashioned.
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