Definition of black bag:
(n) :
(UK, Ireland) A black plastic sack produced for the disposal of household waste.
(n) :
(chiefly US) The pouch or case traditionally carried by medical doctors, especially when making house calls, and containing medical instruments and supplies.
(n) :
A pouch or case containing burglary tools.
(n) :
Synonym of football (“the leather briefcase containing classified nuclear war plans which is always near the US President”)
(adj) :
Alternative spelling of black-bag. [Involving sophisticated clandestine methods for gaining unauthorized entry and obtaining information.]