The most common and most likely answer to this crossword clue is the 11 letter word DEVASTATION
I've seen this crossword clue in The Daily Telegraph
D
E
V
A
S
T
A
T
I
O
N
Buddy explains!
The straight part
We know that "chaos" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case chaos = devastation.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.
What does DEVASTATION mean?
DEVASTATION noun- The act of devastating, or the state of being devastated; a laying waste.
- Waste or misapplication of the assets of a deceased person by an executor or administrator; devastavit.