The most common and most likely answer to this crossword clue is the 10 letter word ILL-SUITED
I've seen this crossword clue in The Times
I
L
L
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S
U
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D
Buddy explains!
The straight part
We know that "not a good match" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not a good match = ill-suited.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 ILL-SUITED mean?
ILL-SUITED adjective- Unsuitable, unfit or inappropriate for some purpose
- Not suiting each other; poorly matched