Double stranded adapters can be synthesized to have blunt ends to both terminals or to have sticky end at one end and blunt end at the other. For instance, a double stranded DNA adapter can be used to link the ends of two other DNA molecules (i.e., ends that do not have "sticky ends", that is complementary protruding single strands by themselves).
Double-stranded DNA adapters can be designed with either blunt or sticky ends.  For example, they can be used to join two DNA molecules that don't have complementary overhangs.