The Collaborative International Dictionary of English v.0.48:

Ataxic \A*tax"ic\, a. [Cf. F. ataxique. See Ataxia.] (Med.)
   Characterized by ataxy, that is,
   (a) by great irregularity of functions or symptoms, or
   (b) by a lack of coordinating power in movements.
       [1913 Webster]

   Ataxic fever, malignant typhus fever. --Pinel.
      [1913 Webster]