The Collaborative International Dictionary of English v.0.48:

Impresario \Im`pre*sa"ri*o\, n.; pl. Impresarios. [It., from
   impresa enterprise.]
   1. The projector, manager, or conductor, of an opera or
      concert company.
      [1913 Webster]

   2. Hence, broadly: Any manager who organizes performances of
      a group.
      [PJC]

WordNet (r) 3.0 (2006):

impresario
    n 1: a sponsor who books and stages public entertainments [syn:
         showman, promoter, impresario]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "impresario":
   MC, administrator, agent, auteur, ballyhoo man, barker, callboy,
   conductor, costume designer, costumer, costumier, deputy,
   directeur, director, emcee, equestrian director, exhibitor,
   governor, intendant, makeup man, manager, master of ceremonies,
   playreader, producer, prompter, rector, responsible person,
   ringmaster, scenewright, set designer, showman, spieler,
   stage director, stage manager, supercargo, theater man,
   theatrician, ticket collector, usher, usherer, usherette