Crook has left mixture (5)
I believe the answer is:
blend
'mixture' is the definition.
(I know that blend is a type of mixture)
'crook has left' is the wordplay.
'crook' becomes 'bend' (synonyms).
'has' is an insertion indicator.
'left' becomes 'l' (common abbreviation).
'bend' going around 'l' is 'BLEND'.
(Other definitions for blend that I've seen before include "Combine together" , "Thorough mixture" , "Amalgam" , "union" , "Amalgamate" .)