The most common and most likely answer to this crossword clue is the 5 letter word GLOOM
I've seen this crossword clue in The Guardian
G
L
O
O
M
More clues leading to the result GLOOM
- Initially glimpsed weaving machine in partial darkness
- Dark brush changing hands
- Grand Master holds game in darkness
- Despondency of Grand Master drawing in game
- Far side in cooling tower is dark
- Beijing’s ultimate spin machine alternative? That’s depressing
- Lack of optimism partly affecting loo manufacturers
- Despondency of union member after swapping sides?
- Good weaver of yarns in the twilight
- Dark girl can get married
Buddy explains!

The straight part
We know that "Dark" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dark = gloom.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 GLOOM mean?
GLOOM noun- Darkness, dimness or obscurity.
- A melancholic, depressing or despondent atmosphere.
- Cloudiness or heaviness of mind; melancholy; aspect of sorrow; low spirits; dullness.
- A drying oven used in gunpowder manufacture.
- To be dark or gloomy.
- To look or feel sad, sullen or despondent.
- To render gloomy or dark; to obscure; to darken.
- To fill with gloom; to make sad, dismal, or sullen.
- To shine or appear obscurely or imperfectly; to glimmer.