1. [n]  large tough non-rigid bag filled with gas or hot air
2. [n]  small thin inflatable rubber bag with narrow neck
3. [v]  become inflated; "The sails ballooned"
4. [v]  ride in a hot air balloon

BALLOON is a 7 letter word that starts with B.

1. \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.
   2. (Arch.) A ball or globe on the top of a pillar, church,
      etc., as at St. Paul's, in London. [R.]
   3. (Chem.) A round vessel, usually with a short neck, to hold
      or receive whatever is distilled; a glass vessel of a
      spherical form.
   4. (Pyrotechnics) A bomb or shell. [Obs.]
   5. A game played with a large inflated ball. [Obs.]
   6. (Engraving) The outline inclosing words represented as
      coming from the mouth of a pictured figure.
   {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.
   

2. \Bal*loon"\, v. t.
   To take up in, or as if in, a balloon.
   

3. \Bal*loon"\, v. i.
   1. To go up or voyage in a balloon.
   2. To expand, or puff out, like a balloon.