The Collaborative International Dictionary of English v.0.48:

black market \black market\ n.
   1. the illicit buying and selling of goods, in violation of
      price controls, rationing, tax laws, prohibition of sale,
      etc.
      [PJC]

   2. a place where such illegal commerce is conducted, or the
      entire system of such illicit commerce considered as a
      whole; as, the black market accounts for twenty percent of
      the Ukrainian economy.
      [PJC]

WordNet (r) 3.0 (2006):

black market
    n 1: people who engage in illicit trade
    2: an illegal market in which goods or currencies are bought and
       sold in violation of rationing or controls
    v 1: deal in illegally, such as arms or liquor [syn: run,
         black market]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "black market":
   Cosa Nostra, Mafia, actionable, against the law, anarchic,
   anarchistic, anomic, black-marketeer, bootleg, bootlegging,
   chargeable, contraband, contrary to law, criminal, felonious,
   fence, flawed, gambling, gray market, illegal, illegal commerce,
   illegal operations, illegitimate, illegitimate business, illicit,
   illicit business, impermissible, irregular, justiciable, lawless,
   loan-sharking, moonshine, moonshining, narcotics traffic,
   nonconstitutional, nonlegal, nonlicit, organized crime, outlaw,
   outlawed, prostitution, protection racket, punishable, push,
   racket, shady dealings, shove, the rackets, the syndicate,
   traffic in women, triable, unallowed, unauthorized,
   unconstitutional, under-the-counter, under-the-table, unlawful,
   unofficial, unstatutory, unwarrantable, unwarranted, usury,
   white slavery, wrongful