The Collaborative International Dictionary of English v.0.48:

Ballooning \Bal*loon"ing\, n.
   1. The art or practice of managing balloons or voyaging in
      them; the sport of riding in balloons.

   Syn: balloonry (archaic)
        [1913 Webster +PJC]

   2. (Stock Exchange) The process of temporarily raising the
      value of a stock, as by fictitious sales. [U.S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

ballooning
    n 1: flying in a balloon

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "ballooning":
   access, accession, accretion, accrual, accruement, accumulation,
   addition, advance, aeronautics, aggrandizement, air service,
   airline, amplification, appreciation, ascent, astronautics,
   augmentation, aviation, bagging, baggy, bellying, billowing,
   billowy, blind flying, bloated, bloating, boom, boost, bosomy,
   broadening, buildup, bulbose, bulbous, bulging, bumped, bumpy,
   bunched, bunchy, cloud-seeding, commercial aviation,
   contact flying, crescendo, cruising, development, distended,
   drooping, droopy, edema, elevation, enlargement, expansion,
   extension, flight, flood, floppy, flying, gain, general aviation,
   gliding, greatening, growth, gush, hike, hillocky, hummocky,
   increase, increment, inflation, jump, leap, limp, loose, lop,
   lop-eared, loppy, mounting, moutonnee, multiplication, nodding,
   pilotage, pneumatic, potbellied, pouching, productiveness,
   proliferation, raise, rise, rounded, sagging, sagging in folds,
   saggy, sailing, sailplaning, snowballing, soaring, spread, surge,
   swag, swelling, tumescence, up, upping, upsurge, upswing, uptrend,
   upturn, verrucated, verrucose, warty, waxing, widening, winging