The Collaborative International Dictionary of English v.0.48:

cha-cha \cha-cha\ n.
   a modern ballroom dance from Latin America; it uses two slow
   steps followed by three quick small steps, with swaying
   movements of the hips, and has many variations of movements
   based on that rhythm.

   Syn: cha-cha.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

cha-cha
    n 1: a modern ballroom dance from Latin America; small steps and
         swaying movements of the hips [syn: cha-cha, cha-cha-
         cha]
    v 1: dance the cha-cha