house of cards

Noun

house of cards (plural houses of cards)

1. A structure made by stacking playing cards in a pyramidal fashion.
2. (attributive, broadly, often) Any structure with alternating vertical and horizontal layers.
   • The essentials of megalithic construction are either the single large slab or the large slab as walling stone with another large slab resting on two or more large walling stones as a capstone—a sort of house of cards architecture.1958, Glyn Edmund Daniel, The Megalith Builders of Western Europe, page 18
   • Dolmens impress only by their massiveness: their house-of-cards construction is the simplest possible […]1977, Lionel Casson, Joseph Jacobs Thorndike, Mysteries of the past, page 49
3. (figuratively, idiomatic) A structure, argument, or arrangement that is inherently flimsy or fragile and thus might collapse if any adversity were to come along and challenge it.