The Collaborative International Dictionary of English v.0.48:

Gusto \Gus"to\, n. [It. or Sp., fr. L. gustus; akin to E.
   choose. Cf. 2d Gust, Go[^u]t.]
   Nice or keen appreciation or enjoyment; relish; taste; fancy;
   as, he ate it with gusto. --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gusto
    n 1: vigorous and enthusiastic enjoyment [syn: gusto,
         relish, zest, zestfulness]