The most common and most likely answer to this crossword clue is the 10 letter word PEACEMAKER
I've seen this crossword clue in The Daily Telegraph
P
E
A
C
E
M
A
K
E
R
More clues leading to the result PEACEMAKER
Buddy explains!

The straight part
We know that "arbitrator" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case arbitrator = peacemaker.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 PEACEMAKER mean?
PEACEMAKER noun- One who sets the pace in a race, to guide the others.
- A set of nerves which stimulate the heart to beat.
- (hence) A medical implement that is used to stimulate a heart to beat by simulating the action of the natural pacemaker.
- A person who restores peace, especially by settling disputes.