The most common and most likely answer to this crossword clue is the 5 plus 2 plus 5 letter word HOUSE OF CARDS
I've seen this crossword clue in The Daily Telegraph
H
O
U
S
E
O
F
C
A
R
D
S
More clues leading to the result HOUSE OF CARDS
- Collection featuring suits — it may not last long!
- Cash used for old, decrepit building that might fall over
- TV series of course had to be edited before screening starts
- Casino’s flimsy structure?
- Unstable deck?
- Built on shaky ground, of course had shifted seconds later
- Unstable structure had of course to be rebuilt with son
- Comedy theatre, conceivably, that’s liable to fold
Buddy explains!
The straight part
We know that "Unstable structure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unstable structure = house of cards.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.