ETYM Cf. Dutch bobbel, Dan. boble, Swed. bubbla. Related to Blob.
A hollow globule of gas (e.g., air or carbon dioxide).
1. A small globule typically hollow and light: as a small body of gas within a liquid; a thin film of liquid inflated with air or gas; a globule in a transparent solid; something (as a plastic or inflatable structure) that is hemispherical or semicylindrical.
2. Something that lacks firmness, solidity, or reality; A delusive scheme.
3. A sound like that of bubbling.
4. magnetic bubble.
5. A state of booming economic activity (as in a stock market) that often ends in a sudden collapse.
6. The condition of being at risk of exclusion or replacement (as from a tournament) — usually used in the phrase on the bubble.

To form produce, or emit bubbles, as of liquids or gases.