The Collaborative International Dictionary of English v.0.48:

Apyrexia \Ap`y*rex"i*a\, Apyrexy \Ap`y*rex`y\, n. [NL. apyrexia,
   fr. Gr. ?; 'a priv. + ? to be feverish, fr. ? fire: cf. F.
   apyrexie.] (Med.)
   The absence or intermission of fever.
   [1913 Webster]