The most common and most likely answer to this crossword clue is the 3 plus 3 plus 3 letter word ODD ONE OUT
I've seen this crossword clue in The Guardian
O
D
D
O
N
E
O
U
T
More clues leading to the result ODD ONE OUT
- Person who’s left dangerous dose finished unconscious
- Something remaining occupied after emptying, and spring-cleaned
- Nonconformist Party: overthrown, finished and no longer in power
- They don’t fit plywood, done outside or inside
- Unconscious after excess drug taken? An anomalous response
- Poem about Spanish gentleman abroad is unlike any other
Buddy explains!
The straight part
We know that "unlike any other" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unlike any other = odd one out.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.