The Collaborative International Dictionary of English v.0.48:

Regatta \Re*gat"ta\ (r?*g?t"t?), n.; pl. Regattas (-t?z). [It.
   regatta, regata.]
   Originally, a gondola race in Venice; now, a rowing or
   sailing race, or a series of such races.
   [1913 Webster]

WordNet (r) 3.0 (2006):

regatta
    n 1: a meeting for boat races