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]