Unstable gambling den? (5,2,5)
I believe the answer is:
house of cards
'unstable gambling den?' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
This is all the clue.
Can you help me to learn more?
(Other definitions for house of cards that I've seen before include "building that might fall over" , "Flimsy structure" , "Unstable scheme" .)