The most common and most likely answer to this crossword clue is the 9 letter word SLAUGHTER
I've seen this crossword clue in Independent
S
L
A
U
G
H
T
E
R
More clues leading to the result SLAUGHTER
- Butcher starting to sell best medicine?
- Killing earl’s thug arranged
- Easily overcome reaction of disgust in alternative to Thatcher?
- Large huts collapsing, in which many die
- Massacre earl’s thug arranged
- Clobber that’s horrible, one criticising clothing
- Take out child, heading off after school on vacation
- Execute composition of Elgar thus
- Butcher beginning to scream, shrieking
- Killing Joke’s aim’s to follow show’s headliner
Buddy explains!

The straight part
We know that "Massacre" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case massacre = slaughter.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 SLAUGHTER mean?
SLAUGHTER noun- The killing of animals, generally for food.
- A massacre; the killing of a large number of people.
- A rout or decisive defeat.
- To butcher animals, generally for food
- To massacre people in large numbers
- To kill in a particularly brutal manner