The Collaborative International Dictionary of English v.0.48:

Black belt \Black" belt`\ (bl[a^]k"b[e^]lt`), n. (Martial arts)
   a comedy that treats of morbid, tragic, gloomy, or grotesque
   situations as a major element of the plot.
   [PJC]

WordNet (r) 3.0 (2006):

black belt
    n 1: a person who attained the rank of expert in the martial
         arts (judo or karate)
    2: a black sash worn to show expert standards in the martial
       arts (judo or karate)

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "black belt":
   Chinese boxer, agricultural region, arable land, bantamweight,
   boxer, brown belt, bruiser, citrus belt, corn belt, cotton belt,
   countryside, dust bowl, farm belt, farm country, farmland,
   featherweight, fighter, fisticuffer, flyweight, fruit belt,
   grass roots, grassland, grazing region, heavyweight, highlands,
   karate expert, light heavyweight, lightweight, lowlands,
   meadows and pastures, middleweight, moors, palooka, plains,
   prairies, prizefighter, province, provinces, pug, pugilist,
   rural district, rustic region, savate expert, sparrer, steppes,
   the country, the soil, the sticks, tobacco belt, uplands, veld,
   welterweight, wheat belt, wide-open spaces, woodland,
   woods and fields, yokeldom