The Collaborative International Dictionary of English v.0.48:

nada \nada\ n.
   1. [Spanish] Nothing. [informal or jocose]

   Note: [used mostly jocosely or for emphasis in phrases such
         as "Nothing, nada, zip!"]
         [PJC]

WordNet (r) 3.0 (2006):

nada
    n 1: a quantity of no importance; "it looked like nothing I had
         ever seen before"; "reduced to nil all the work we had
         done"; "we racked up a pathetic goose egg"; "it was all for
         naught"; "I didn't hear zilch about it" [syn: nothing,
         nil, nix, nada, null, aught, cipher, cypher,
         goose egg, naught, zero, zilch, zip, zippo]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "nada":
   aught, cipher, goose egg, naught, nichts, nihil, nihility, nil,
   nix, no such thing, nonexistence, nothing, nothing at all,
   nothing on earth, nothing whatever, nullity, thing of naught,
   vacuity, zero, zilch