The most common and most likely answer to this crossword clue is the 12 letter word DISCOMPOSURE
I've seen this crossword clue in The Times
D
I
S
C
O
M
P
O
S
U
R
E
More clues leading to the result DISCOMPOSURE
- Dip, ours, comes unexpectedly bringing unease
- Dance club certain about politician and old disturbance
- Club certainly involving old politician’s agitation
- Unease of party politician with nothing certain
- Party politician, with nothing certain, showing unease
- Old politician in party certain to generate unease
- Upset with disclosure when old member’s out for fifty
Buddy explains!

The straight part
We know that "disturbance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case disturbance = discomposure.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 DISCOMPOSURE mean?
DISCOMPOSURE noun- The state of being discomposed.
- Discordance; disagreement of parts.