The most common and most likely answer to this crossword clue is the 8 letter word BUTCHERY
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More clues leading to the result BUTCHERY
Buddy explains!

The straight part
We know that "killing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case killing = butchery.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 BUTCHERY mean?
BUTCHERY noun- The cruel, ruthless killings of humans, as at a slaughterhouse.
- An abattoir, a slaughterhouse.
- The butchering of meat.
- A disastrous effort, an atrocious failure.
- A meat market
- The stereotypical behaviors and accoutrements of being a butch lesbian.