Noun

1. A hollow globule of gas (e.g., air or carbon dioxide)
2. A speculative scheme that depends on unstable factors that the planner cannot control
3. An impracticable and illusory idea
4. A dome-shaped covering made of transparent glass or plastic

Verb

1. Form, produce, or emit bubbles
2. Flow in an irregular current with a bubbling noise
3. Rise in bubbles or as if in bubbles
4. Cause to form bubbles
5. Expel gas from the stomach