1.Definition: a dome-shaped covering made of transparent glass or plastic

Category: Objects

2.Definition: a hollow globule of gas (e.g., air or carbon dioxide)

Category: Objects

3.Definition: a speculative scheme that depends on unstable factors that the planner cannot control

"His proposal was nothing but a house of cards", "A real estate bubble"

Category: General

4.Definition: an impracticable and illusory idea

"He didn't want to burst the newcomer's bubble"

Category: General