Source : Webster's Revised Unabridged Dictionary (1913)

Bolster \Bol"ster\, v. t. [imp. & p. p. {Bolstered}; p. pr. &
   vb. n. {Bolstering}.]
   1. To support with a bolster or pillow. --S. Sharp.

   2. To support, hold up, or maintain with difficulty or
      unusual effort; -- often with up.

            To bolster baseness.                  --Drayton.

            Shoddy inventions designed to bolster up a
            factitious pride.                     --Compton
                                                  Reade.

Bolster \Bol"ster\, n. [AS. bolster; akin to Icel. b?lstr, Sw. &
   Dan. bolster, OHG. bolstar, polstar, G. polster; from the
   same root as E. bole stem, bowl hollow vessel. Cf. {Bulge},
   {Poltroon}.]
   1. A long pillow or cushion, used to support the head of a
      person lying on a bed; -- generally laid under the
      pillows.

            And here I'll fling the pillow, there the bolster,
            This way the coverlet, another way the sheets.
                                                  --Shak.

   2. A pad, quilt, or anything used to hinder pressure, support
      any part of the body, or make a bandage sit easy upon a
      wounded part; a compress.

            This arm shall be a bolster for thy head. --Gay.

   3. Anything arranged to act as a support, as in various forms
      of mechanism, etc.

   4. (Saddlery) A cushioned or a piece part of a saddle.

   5. (Naut.)
      (a) A cushioned or a piece of soft wood covered with
          tarred canvas, placed on the trestletrees and against
          the mast, for the collars of the shrouds to rest on,
          to prevent chafing.
      (b) Anything used to prevent chafing.

   6. A plate of iron or a mass of wood under the end of a
      bridge girder, to keep the girder from resting directly on
      the abutment.

   7. A transverse bar above the axle of a wagon, on which the
      bed or body rests.

   8. The crossbeam forming the bearing piece of the body of a
      railway car; the central and principal cross beam of a car
      truck.

   9. (Mech.) the perforated plate in a punching machine on
      which anything rests when being punched.

   10. (Cutlery)
       (a) That part of a knife blade which abuts upon the end
           of the handle.
       (b) The metallic end of a pocketknife handle. --G.
           Francis.

   11. (Arch.) The rolls forming the ends or sides of the Ionic
       capital. --G. Francis.

   12. (Mil.) A block of wood on the carriage of a siege gun,
       upon which the breech of the gun rests when arranged for
       transportation.

   Note: [See Illust. of {Gun carriage}.]

   {Bolster work} (Arch.), members which are bellied or curved
      outward like cushions, as in friezes of certain classical
      styles.

Source : WordNet®

bolster
     v 1: support and strengthen; "bolster morale" [syn: {bolster up}]
     2: prop up with a pillow or bolster
     3: add padding to; "pad the seat of the chair" [syn: {pad}]

bolster
     n : a pillow that is often put across a bed underneath the
         regular pillows [syn: {long pillow}]