The most common and most likely answer to this crossword clue is the 7 letter word TARNISH
I've seen this crossword clue in The Guardian
T
A
R
N
I
S
H
More clues leading to the result TARNISH
- Lose lustre: rather like small mountain lake?
- Dull, like a mountain lake?
- Stain bottom of post with gloss, not top
- Lose brightness like small mountain lake?
- Dirty shirt, short and tight
- Water is hot giving discolouration
- Rock star in hot spot
- Dirty, like a small lake?
- This mountain feature is hard to spot
- Dull mountain lake of a sort?
Buddy explains!
The straight part
We know that "Dirty" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dirty = tarnish.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 TARNISH mean?
TARNISH noun- Oxidation or discoloration, especially of a decorative metal exposed to air.
- To oxidize or discolor due to oxidation.
- To soil, sully, damage or compromise
- To lose its lustre or attraction; to become dull.