The most common and most likely answer to this crossword clue is the 11 letter word ILL-DEFINED
I've seen this crossword clue in The Guardian
I
L
L
-
D
E
F
I
N
E
D
More clues leading to the result ILL-DEFINED
Buddy explains!
The straight part
We know that "Dim" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dim = ill-defined.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-DEFINED mean?
ILL-DEFINED adjective- Poorly defined; blurry, out of focus; lacking a clear boundary.
- Defined in an inconsistent way.