King has horse slaughtered and ritually prepared (6)
I believe the answer is:
kosher
'ritually prepared' is the definition.
(prepared according to Jewish law)
'king has horse slaughtered' is the wordplay.
'king' becomes 'K' (abbreviation for king in chess).
'has' says to put letters next to each other.
'slaughtered' is an anagram indicator.
'horse' is an anagram of 'osher'.
'k'+'osher'='KOSHER'
'and' is the link.
(Other definitions for kosher that I've seen before include "(Of food) meeting Jewish dietary law" , "Ritually clean (food)" , "Legitimate (Jewish food)" , "Edible for Jew" , "In accordance with Jewish law" .)