Definition of: balloon

(bə·ln′) noun
1. A large, airtight bag, inflated with gas lighter than air, designed to rise and float in the atmosphere: larger kinds have a car or basket attached, for carrying passengers, instruments, etc. Compare DIRIGIBLE, BLIMP.
2. A small inflatable rubber bag, used as a toy.
3. Chem. A spherical glass vessel.
4. A balloon-shaped outline connected with the mouth of a person, containing the words he is represented as speaking, as in comic strips.
—captive balloon A balloon restrained from free flight by means of a cable that holds it to the ground.
—kite balloon An elongated form of captive balloon, fitted with a tail appendage to keep it headed into the wind.
—observation balloon A captive balloon used as an observation post.
—sounding balloon A balloon sent up unmanned for obtaining meteorological data recorded on instruments which return to earth after the bursting of the balloon. Compare RADIOSONDE.
—v.i.
1. To increase quickly in scope or magnitude; expand: The rumor ballooned into a scandal.
2. To swell out like a balloon, as a sail.
3. To travel or ascend in a balloon.
—v.t.
4. To inflate or swell with air: A gust of wind ballooned the sail. [<Ital. ballone large ball <balla ball, sphere <Gmc.]
—bal·loon′ist noun