The most common and most likely answer to this crossword clue is the 10 letter word COMPETITOR
I've seen this crossword clue in The Daily Telegraph
C
O
M
P
E
T
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T
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R
More clues leading to the result COMPETITOR
- . Rival firm without any English flier, work uncovered
- Player with little French put into cold changing room
- Rival clubs locking small Parisian in changing room
- Entrant in race scheming to crop time
- Rival clubs promote changes covering it
- Rival school’s tie twisted round bunk
- Knock down price — motto of rival trader?
Buddy explains!
The straight part
We know that "rival trader" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rival trader = competitor.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.
Crossword Answer definitions
COMPETITOR noun- A person or organization against whom one is competing.
- A participant in a competition, especially in athletics.