Bubble  —n. 1 a thin sphere of liquid enclosing air etc. B air-filled cavity in a liquid or solidified liquid. 2 transparent domed canopy. 3 visionary or unrealistic project. —v. (-ling) 1 rise in or send up bubbles. 2 make the sound of boiling.  bubble over (often foll. By with) be exuberant. [imitative]