The Collaborative International Dictionary of English v.0.48:

Plaster \Plas"ter\, n. [AS., a plaster (in sense 1), fr. L.
   emplastrum, Gr. ?, ?, fr. ? to daub on, stuff in; ? in + ? to
   mold: cf. OF. plastre a plaster (in sense 2), F. pl[^a]tre.
   Cf. Plastic, Emplaster, Piaster.] [Formerly written
   also plaister.]
   1. (Med.) An external application of a consistency harder
      than ointment, prepared for use by spreading it on linen,
      leather, silk, or other material. It is adhesive at the
      ordinary temperature of the body, and is used, according
      to its composition, to produce a medicinal effect, to bind
      parts together, etc.; as, a porous plaster; sticking
      plaster.
      [1913 Webster]

   2. A composition of lime, water, and sand, with or without
      hair as a bond, for coating walls, ceilings, and
      partitions of houses. See Mortar.
      [1913 Webster]

   3. Calcined gypsum, or plaster of Paris, especially when
      ground, as used for making ornaments, figures, moldings,
      etc.; or calcined gypsum used as a fertilizer.
      [1913 Webster]

   Plaster cast, a copy of an object obtained by pouring
      plaster of Paris mixed with water into a mold.

   Plaster of Paris. [So called because originally brought
      from a suburb of Paris.] (Chem.) Anhydrous calcium
      sulphate, or calcined gypsum, which forms with water a
      paste which soon sets or hardens, and is used for casts,
      moldings, etc. The term is loosely applied to any plaster
      stone or species of gypsum.

   Plaster of Paris bandage (Surg.), a bandage saturated with
      a paste of plaster of Paris, which on drying forms a
      perfectly fitting splint.

   Plaster stone, any species of gypsum. See Gypsum.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plaster \Plas"ter\, v. t. [imp. & p. p. Plastered; p. pr. &
   vb. n. Plastering.] [Cf. OF. plastrer to plaster (in sense
   2), F. pl[^a]trer.]
   1. To cover with a plaster, as a wound or sore.
      [1913 Webster]

   2. To overlay or cover with plaster, as the ceilings and
      walls of a house.
      [1913 Webster]

   3. Fig.: To smooth over; to cover or conceal the defects of;
      to hide, as with a covering of plaster. --Bale.
      [1913 Webster]

WordNet (r) 3.0 (2006):

plaster
    n 1: a mixture of lime or gypsum with sand and water; hardens
         into a smooth solid; used to cover walls and ceilings
    2: any of several gypsum cements; a white powder (a form of
       calcium sulphate) that forms a paste when mixed with water
       and hardens into a solid; used in making molds and sculptures
       and casts for broken limbs [syn: plaster of Paris,
       plaster]
    3: a medical dressing consisting of a soft heated mass of meal
       or clay that is spread on a cloth and applied to the skin to
       treat inflamed areas or improve circulation etc. [syn:
       poultice, cataplasm, plaster]
    4: a surface of hardened plaster (as on a wall or ceiling);
       "there were cracks in the plaster" [syn: plaster,
       plasterwork]
    5: adhesive tape used in dressing wounds [syn: plaster,
       adhesive plaster, sticking plaster]
    v 1: apply a heavy coat to [syn: plaster, plaster over,
         stick on]
    2: cover conspicuously or thickly, as by pasting something on;
       "The demonstrators plastered the hallways with posters"; "She
       let the walls of the apartment be beplastered with stucco"
       [syn: plaster, beplaster]
    3: affix conspicuously; "She plastered warnings all over the
       wall"
    4: apply a plaster cast to; "plaster the broken arm"
    5: coat with plaster; "daub the wall" [syn: plaster, daub]
    6: dress by covering with a therapeutic substance [syn:
       poultice, plaster]

Moby Thesaurus II by Grady Ward, 1.0:

179 Moby Thesaurus words for "plaster":
   Ace bandage, Band-Aid, Portland cement, Spackle, adherent,
   adhesive, adhesive tape, adobe, application, ashlar, band, bandage,
   bandaging, barnacle, bathe, bedaub, besmear, binder, booze up,
   boozify, brace, bramble, brick, bricks and mortar, brier, bulldog,
   burr, butter, care for, cast, cataplasm, cement, chinking, clay,
   clinker, coat, composition, compress, concrete, cotton,
   court plaster, cover, covering materials, cravat, crock, crush,
   cure, dab, daub, decal, decalcomania, dental pulp, diagnose,
   doctor, drag, dress, dressing, dub, elastic bandage, epithem,
   equalize, even, ferroconcrete, firebrick, flag, flagstone, flatten,
   flooring, flux, four-tailed bandage, fuddle, gauze, give care to,
   glue, grade, grease, grout, gunk, harrow, heal, lath and plaster,
   lay, leech, level, limpet, lint, lubricate, mash, masonry, massage,
   mastic, minister to, molasses, mortar, mow, mucilage, mush, nurse,
   oil, operate on, overlay, overtake, paper pulp, parget, paste,
   patching plaster, pavement, paving, paving material, physic,
   pickle, pith, plane, planish, plaster cast, plasters, pledget,
   pollute, porridge, poultice, prestressed concrete, prickle,
   pudding, pulp, pulp lead, pulpwood, purge, rag pulp, remedy,
   remora, roller, roller bandage, roofage, roofing, roughcast, rub,
   rubber bandage, sauce, shave, siding, size, sling, smarm, smash,
   smear, smooth, smooth down, smooth out, smudge, souse,
   spackling compound, splint, sponge, spread, squash, stew, sticker,
   stone, strap, stucco, stupe, sulfate pulp, sulfite pulp,
   superimpose, swack, syrup, tampon, tape, tent, thorn, tile, tiling,
   tipsify, tourniquet, treat, triangular bandage, walling,
   white lead, wood pulp