The most common and most likely answer to this crossword clue is the 5 letter word HAVOC
I've seen this crossword clue in The Times
H
A
V
O
C
More clues leading to the result HAVOC
- Shrink with a vocation causing mayhem
- Dreadful chaos, mostly — very?
- Vulgar young person losing head confronts superior officer — big trouble
- Own contracting business overcoming disruption
- Temperature settings protecting a very old ruin
- Unruly chav gains nothing, causing disruption
- Unruly leaders of Viking hordes often cause absolute chaos
- There’s chaos when one plays this
- Henry’s a brave man taking over in chaos
- In Messiah a vocal part creates confusion
Buddy explains!

The straight part
We know that "Dreadful chaos, mostly — very" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dreadful chaos, mostly — very = havoc.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 HAVOC mean?
HAVOC noun- Widespread devastation, destruction
- Mayhem
- To pillage.
- To cause havoc.
- A cry in war as the signal for indiscriminate slaughter.