Bal•loon /be'lōōn/ Noun 1.) a brightly colored rubber sac inflated withe air then sealed at the neck, used a a children's toy or a decoration. 2.) a large bag filled with hot air or gas to make it rise in the air, typically carrying a basket of passengers. "She was in a ditch known as depression waiting for a balloon to save her from the darkness." Synonyms: hot-air ballon, barrage ballon, more...