The most common and most likely answer to this crossword clue is the 9 letter word OBSCUREST
I've seen this crossword clue in The Times
O
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More clues leading to the result OBSCUREST
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The straight part
We know that "Extremely dim" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extremely dim = obscurest.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 OBSCUREST mean?
OBSCUREST verb- To render obscure; to darken; to make dim; to keep in the dark; to hide; to make less visible, intelligible, legible, glorious, beautiful, or illustrious.
- To hide, put out of sight etc.
- To conceal oneself; to hide.
- Dark, faint or indistinct.
- Hidden, out of sight or inconspicuous.
- Difficult to understand.
- Not well-known.
- Unknown or uncertain; unclear.