The Collaborative International Dictionary of English v.0.48:

Ataxia \A*tax"i*a\, Ataxy \At"ax*y\, n. [NL. ataxia, Gr. ?, fr.
   ? out of order; 'a priv. + ? ordered, arranged, ? to put in
   order: cf. F. ataxie.]
   1. Disorder; irregularity. [Obs.] --Bp. Hall.
      [1913 Webster]

   2. (Med.)
      (a) Irregularity in disease, or in the functions.
      (b) The state of disorder that characterizes nervous
          fevers and the nervous condition. [archaic]
          [1913 Webster]

   3. (Med.) Loss of coordination in the voluntary muscles,
      especially the limbs; an inability to coordinate voluntary
      muscle movements; it results in unsteady movements and a
      staggering gait. See also locomotor ataxia, an ataxia
      which occurs when attempting to perform coordinated
      muscular movements.

   Syn: ataxy
        [WordNet 1.5 +PJC]

   Locomotor ataxia. See Locomotor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ataxia
    n 1: inability to coordinate voluntary muscle movements;
         unsteady movements and staggering gait [syn: ataxia,
         ataxy, dyssynergia, motor ataxia]