Crime in the game Clue (6)
I believe the answer is:
murder
'crime in the game clue' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for murder that I've seen before include "Serious crime (that may be blue?)" , "Killing most foul" , "Unlawful premeditated killing" , "very difficult task" , "See 20" .)