Balloon  —n. 1 small inflatable rubber toy or decoration. 2 large usu. Round inflatable flying bag, often carrying a basket for passengers. 3 colloq. Balloon shape enclosing dialogue etc. In a comic strip or cartoon. —v. 1 (cause to) swell out like a balloon. 2 travel by balloon.  balloonist n. [french or italian, = large ball]