The most common and most likely answer to this crossword clue is the 8 letter word MOURNFUL
M
O
U
R
N
F
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L
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The straight part
We know that "Gloomy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gloomy = mournful.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 MOURNFUL mean?
MOURNFUL adjective- Filled with grief or sadness; being in a state in which one mourns.
- Fit to inspire mourning; tragic.