soap bubble

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A bubble, especially a large one, formed from soapy water.
2. n. Something beautiful but transient or illusory.

Century Dictionary and Cyclopedia

1. n. A bubble formed from soapy water; especially, a thin spherical film of soap-suds inflated by blowing through a pipe, and forming a hollow globe which has often beautiful iridescent colors playing over the surface.

Wiktionary

1. n. A very thin film of soap water that forms a sphere with an iridescent surface.

GNU Webster's 1913

1. n. a hollow iridescent globe, formed by blowing a film of soap suds from a pipe; figuratively, something attractive, but extremely unsubstantial.

WordNet 3.0

1. n. a bubble formed by a thin soap film