Double-Dutch criminal? (8)
I believe the answer is:
bigamist
'criminal?' is the definition.
(someone married to more than one person)
I cannot understand how the remainder of the clue works.
(Other definitions for bigamist that I've seen before include "Person who marries illegally - already wed (8)" , "Man with two wives" , "One marrying too often" , "member of two unions" , "lawbreaking union member" .)