The Collaborative International Dictionary of English v.0.48:

Vehicle \Ve"hi*cle\, n. [L. vehiculum, fr. vehere to carry; akin
   to E. way, wain. See Way, n., and cf. Convex, Inveigh,
   Veil, Vex.]
   [1913 Webster]
   1. That in or on which any person or thing is, or may be,
      carried, as a coach, carriage, wagon, cart, car, sleigh,
      bicycle, etc.; a means of conveyance; specifically, a
      means of conveyance upon land.
      [1913 Webster]

   2. That which is used as the instrument of conveyance or
      communication; as, matter is the vehicle of energy.
      [1913 Webster]

            A simple style forms the best vehicle of thought to
            a popular assembly.                   --Wirt.
      [1913 Webster]

   3. (Pharm.) A substance in which medicine is taken.
      [1913 Webster]

   4. (Paint.) Any liquid with which a pigment is applied,
      including whatever gum, wax, or glutinous or adhesive
      substance is combined with it.
      [1913 Webster]

   Note: Water is used in fresco and in water-color painting,
         the colors being consolidated with gum arabic; size is
         used in distemper painting. In oil painting, the fixed
         oils of linseed, nut, and poppy, are used; in
         encaustic, wax is the vehicle. --Fairholt.
         [1913 Webster]

   5. (Chem.) A liquid used to spread sensitive salts upon glass
      and paper for use in photography.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

vehicle
    n 1: a conveyance that transports people or objects
    2: a medium for the expression or achievement of something; "his
       editorials provided a vehicle for his political views"; "a
       congregation is a vehicle of group identity"; "the play was
       just a vehicle to display her talents"
    3: any substance that facilitates the use of a drug or pigment
       or other material that is mixed with it
    4: any inanimate object (as a towel or money or clothing or
       dishes or books or toys etc.) that can transmit infectious
       agents from one person to another [syn: fomite, vehicle]

Moby Thesaurus II by Grady Ward, 1.0:

202 Moby Thesaurus words for "vehicle":
   Charlie McCarthy, Grand Guignol, Passion play, Tom show, agency,
   agent, ancilla, antimasque, appliance, audience success, backing,
   ballet, bibliofilm, bipack, black-and-white film, bomb,
   broadcast drama, burlesque show, carrier, cartridge, channel,
   charade, chromogen, cliff hanger, closet drama, coat,
   coat of paint, coating, color, color film, color filter,
   color gelatin, color negative film, colorant, coloring,
   comedy drama, conduit, contrivance, conveyance, creature,
   critical success, daytime serial, dead-color, device, dialogue,
   distemper, documentary drama, dope, drama, dramalogue,
   dramatic play, dramatic series, drier, dry plate, dummy, duodrama,
   duologue, dupe, dye, dyestuff, emulsion, epic theater,
   experimental theater, exterior paint, extravaganza, failure, film,
   flat coat, flat wash, floor enamel, flop, frame, gasser, giveaway,
   go-between, ground, handmaid, handmaiden, happening, hit, hit show,
   implement, improvisational drama, instrument, instrumentality,
   interagent, interior paint, intermediary, intermediate,
   intermedium, legitimate drama, lever, masque, mean, means,
   mechanism, mediator, medium, melodrama, microfilm, midwife, minion,
   ministry, minstrel show, miracle, miracle play, monochromatic film,
   monodrama, monologue, morality, morality play, motion-picture film,
   music drama, musical revue, mystery, mystery play, negative,
   opaque color, opera, organ, orthochromatic film, pack, pageant,
   paint, panchromatic film, panel show, pantomime, pastoral,
   pastoral drama, pawn, photographic paper, piece, pigment, plate,
   play, playlet, plaything, prime coat, primer, priming,
   printing paper, problem play, psychodrama, puppet, quiz show,
   radio drama, review, revue, roll, sensational play, serial,
   servant, show, sitcom, situation comedy, sketch, skit, slave, soap,
   soap opera, sociodrama, sound film, sound track, sound-on-film,
   soundstripe, spectacle, stage play, stage show, stain, stooge,
   straight drama, success, suspense drama, tableau, tableau vivant,
   talk show, teleplay, television drama, television play, tempera,
   theater of cruelty, thinner, tinction, tincture, tool,
   total theater, toy, transparent color, transport, transportation,
   tripack, turpentine, turps, undercoat, undercoating, variety show,
   vaudeville, vaudeville show, wash, wash coat,
   word-of-mouth success, work