Criminal venture to achieve mastery (8)
I believe the answer is:
conquest
'mastery' is the definition.
(thesaurus)
'criminal venture' is the wordplay.
'criminal' becomes 'con' (abbreviation for 'convict').
'venture' becomes 'quest' (both can mean a mission or endeavour).
'con'+'quest'='CONQUEST'
'to achieve' acts as a link.
(Other definitions for conquest that I've seen before include "occupied territory" , "Catch" , "hostile takeover" , "Vanquishment" , "The subjugation and assumption of control by military force" .)