気球

1. Origins, structure, and basic meaning

• Structure: 気球(ききゅう) is an aircraft that floats using a lighter-than-air gas or heated air.
• Basic usage: It names an airborne balloon that rises into the sky or is affected by the wind.

2. Common pitfalls and similar expressions

• Not only hot-air balloons
  • 熱気球 specifically uses heated air. 気球 alone does not establish that the balloon contains hot air.
• Rising and launching
  • 気球が昇る describes the balloon's movement; 気球を飛ばす describes someone launching it.