The Collaborative International Dictionary of English v.0.48:

Pillar \Pil"lar\, a. (Mach.)
   Having a support in the form of a pillar, instead of legs;
   as, a pillar drill.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            Jacob set a pillar upon her grave.    --Gen. xxxv.
                                                  20.
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            The place . . . vast and proud,
            Supported by a hundred pillars stood. --Dryden.
      [1913 Webster]

   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.
      [1913 Webster]

            By day a cloud, by night a pillar of fire. --Milton.
      [1913 Webster]

   3. (R. C. Ch.) A portable ornamental column, formerly carried
      before a cardinal, as emblematic of his support to the
      church. [Obs.] --Skelton.
      [1913 Webster]

   4. (Man.) The center of the volta, ring, or manege ground,
      around which a horse turns.
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   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pillar
    n 1: a fundamental principle or practice; "science eroded the
         pillars of superstition"
    2: anything that approximates 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, pillar]
    3: a prominent supporter; "he is a pillar of the community"
       [syn: pillar, mainstay]
    4: a vertical cylindrical structure standing alone and not
       supporting anything (such as a monument) [syn: column,
       pillar]
    5: (architecture) a tall vertical cylindrical structure standing
       upright and used to support a structure [syn: column,
       pillar]