The Collaborative International Dictionary of English v.0.48:

Balloon \Bal*loon"\, v. t.
   To take up in, or as if in, a balloon.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Balloon \Bal*loon"\, v. i.
   1. To go up or voyage in a balloon.
      [1913 Webster]

   2. To expand, or puff out, like a balloon.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Balloon \Bal*loon"\, n. [F. ballon, aug. of balle ball: cf. It.
   ballone. See 1st Ball, n., and cf. Pallone.]
   1. A bag made of silk or other light material, and filled
      with hydrogen gas or heated air, so as to rise and float
      in the atmosphere; especially, one with a car attached for
      a["e]rial navigation.
      [1913 Webster]

   2. (Arch.) A ball or globe on the top of a pillar, church,
      etc., as at St. Paul's, in London. [R.]
      [1913 Webster]

   3. (Chem.) A round vessel, usually with a short neck, to hold
      or receive whatever is distilled; a glass vessel of a
      spherical form.
      [1913 Webster]

   4. (Pyrotechnics) A bomb or shell. [Obs.]
      [1913 Webster]

   5. A game played with a large inflated ball. [Obs.]
      [1913 Webster]

   6. (Engraving) The outline inclosing words represented as
      coming from the mouth of a pictured figure.
      [1913 Webster]

   Air balloon, a balloon for a["e]rial navigation.

   Balloon frame (Carp.), a house frame constructed altogether
      of small timber.

   Balloon net, a variety of woven lace in which the weft
      threads are twisted in a peculiar manner around the warp.
      [1913 Webster]

WordNet (r) 3.0 (2006):

balloon
    n 1: large tough nonrigid bag filled with gas or heated air
    2: small thin inflatable rubber bag with narrow neck
    v 1: ride in a hot-air balloon; "He tried to balloon around the
         earth but storms forced him to land in China"
    2: become inflated; "The sails ballooned" [syn: balloon,
       inflate, billow]

Moby Thesaurus II by Grady Ward, 1.0:

142 Moby Thesaurus words for "balloon":
   Graf Zeppelin, accrue, accumulate, advance, aeroplane, aerostat,
   air bubble, airlift, airplane, airship, appreciate, bag, ball,
   ballonet, be airborne, bead, belly, belly out, bilge, billow,
   bladder, bleb, blimp, blister, bloat, blob, blood blister, boll,
   bolus, boom, bouge, breed, broaden, bubble, bug, bulb, bulbil,
   bulblet, bulge, bulk, bulla, captive balloon, conglobulate,
   crescendo, cruise, develop, dilate, dirigible, dirigible balloon,
   distend, drift, ellipsoid, enlarge, expand, extend, ferry,
   fever blister, fill out, flit, fly, fob, gain, gain strength,
   gasbag, geoid, get ahead, glide, globe, globelet, globoid, globule,
   glomerulus, go up, gob, gobbet, goggle, greaten, grow, hop, hover,
   hydroplane, increase, intensify, jet, knob, knot,
   lighter-than-air craft, mount, multiply, mushroom, navigate,
   oblate spheroid, orb, orbit, orblet, pellet, pilot balloon, pocket,
   poke, pooch, pop, pouch, pout, prolate spheroid, proliferate,
   puff up, rigid airship, rise, rondure, round out, run up, sac,
   sack, sail, sailplane, sausage, seaplane, semirigid airship, ship,
   shoot up, snowball, soap bubble, soar, sphere, spherify, spheroid,
   spherule, spread, strengthen, stretch, swell, swell out,
   take the air, take wing, tumefy, vesicle, volplane, wax,
   weather balloon, widen, wing, zeppelin