The Collaborative International Dictionary of English v.0.48:

Divertimento \Di*ver`ti*men"to\, n.; pl. -ti. [It.] (Mus.)
   A light and pleasing composition.
   [1913 Webster]

WordNet (r) 3.0 (2006):

divertimento
    n 1: a musical composition in several movements; has no fixed
         form [syn: divertimento, serenade]