The most common and most likely answer to this crossword clue is the 11 letter word ARBITRAGEUR
I've seen this crossword clue in The Daily Telegraph
A
R
B
I
T
R
A
G
E
U
R
More clues leading to the result ARBITRAGEUR
Buddy explains!
The straight part
We know that "Trader" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trader = arbitrageur.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 ARBITRAGEUR mean?
ARBITRAGEUR noun- One who engages in arbitrage, such as a financial broker or an investment bank.