The most common and most likely answer to this crossword clue is the 9 letter word POLLUTION
I've seen this crossword clue in The Guardian
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More clues leading to the result POLLUTION
Buddy explains!
The straight part
We know that "9 this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case 9 this = pollution.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 POLLUTION mean?
POLLUTION noun- The desecration of something holy or sacred; defilement, profanation.
- The ejaculation of semen outside of sexual intercourse, especially a nocturnal emission.
- Moral or spiritual corruption; impurity, degradation, defilement.
- Physical contamination, now especially the contamination of the environment by harmful substances, or by disruptive levels of noise, light etc.
- Something that pollutes; a pollutant.