Source : Webster's Revised Unabridged Dictionary (1913)

Pillar \Pil"lar\, n. [OE. pilerF. pilier, LL. pilare, pilarium,
   pilarius, fr. L. pila a pillar. See {Pile} a heap.]
   1. The general and popular term for a firm, upright,
      insulated support for a superstructure; a pier, column, or
      post; also, a column or shaft not supporting a
      superstructure, as one erected for a monument or an
      ornament.

            Jacob set a pillar upon her grave.    --Gen. xxxv.
                                                  20.

            The place . . . vast and proud, Supported by a
            hundred pillars stood.                --Dryden.

   2. Figuratively, that which resembles such a pillar in
      appearance, character, or office; a supporter or mainstay;
      as, the Pillars of Hercules; a pillar of the state. ``You
      are a well-deserving pillar.'' --Shak.

            By day a cloud, by night a pillar of fire. --Milton.

   3. (R. C. Ch.) A portable ornamental column, formerly carried
      before a cardinal, as emblematic of his support to the
      church. [Obs.] --Skelton.

   4. (Man.) The center of the volta, ring, or manege ground,
      around which a horse turns.

   {From pillar to post}, hither and thither; to and fro; from
      one place or predicament to another; backward and forward.
      [Colloq.]

   {Pillar saint}. See {Stylite}.

   {Pillars of the fauces}. See {Fauces}, 1.

Pillar \Pil"lar\, a. (Mach.)
   Having a support in the form of a pillar, instead of legs;
   as, a pillar drill.

Source : WordNet®

pillar
     n 1: a fundamental principle or practice; "science eroded the
          pillars of superstition"
     2: anything tall and thin approximating the shape of a column
        or tower; "the test tube held a column of white powder";
        "a tower of dust rose above the horizon"; "a thin pillar
        of smoke betrayed their campsite" [syn: {column}, {tower}]
     3: a prominent supporter; "he is a pillar of the community"
        [syn: {mainstay}]
     4: a vertical structure standing alone and not supporting
        anything (as a monument or a column of air) [syn: {column}]
     5: (architeture) a tall cylindrical vertical upright and used
        to support a structure [syn: {column}]