The most common and most likely answer to this crossword clue is the 8 letter word PLACATED
I've seen this crossword clue in The Daily Telegraph
P
L
A
C
A
T
E
D
More clues leading to the result PLACATED
Buddy explains!

The straight part
We know that "Calmed down" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case calmed down = placated.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 PLACATED mean?
PLACATED verb- To calm; to bring peace to; to influence someone who was furious to the point that they become content or at least no longer irate.