Keeping quiet, initiated in slaughter (9)
I believe the answer is:
bloodshed
'slaughter' is the definition.
(I know that bloodshed is a type of slaughter)
'keeping quiet initiated' is the wordplay.
'keeping' means one lot of letters goes inside another.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'initiated' becomes 'blooded' (to blood is to initiate an animal into violence).
'sh' put within 'blooded' is 'BLOODSHED'.
'in' acts as a link.
(Other definitions for bloodshed that I've seen before include "The killing or wounding of people, very gory" , "Indiscriminate slaughter" , "Carnage" .)