soap-bubble

Noun

soap bubble (plural soap bubbles)

1. A very thin film of soapy water that forms a sphere with an iridescent surface.
2. (figuratively) Anything that is attractive but insubstantial.
   • These words so pierce this soap-bubble of the metaphysicians, that we can hardly read them without fancying that the poet meant them to be ironical.1879, John Campbell Shairp, Robert Burns, London: Macmillan