Definitions of balloon:

• noun:   large tough non-rigid bag filled with gas or heated air
• noun:   small thin inflatable rubber bag with narrow neck
• verb:   become inflated

  Example: "The sails ballooned"

• verb:   ride in a hot-air balloon

  Example: "He tried to balloon around the earth but storms forced him to land in China"

• name:  A surname (very rare: popularity rank in the U.S.: #75246)