Swear sheep and lamb play together (9)
I believe the answer is:
blaspheme
'swear' is the definition.
(synonyms)
'sheep and lamb play together' is the wordplay.
'and' says to put letters next to each other.
'play together' is an anagram indicator (letters playing around).
'sheep' put after 'lamb' is 'lambsheep'.
'lambsheep' is an anagram of 'BLASPHEME'.
(Other definitions for blaspheme that I've seen before include "Speak irreverently about God" , "Curse, profane" , "Utter obscenities or profanities" , "Swear" , "Talk irreverently about God and sacred things" .)