opisthotonos

from WordNet (r) 3.0 (2006)

opisthotonos
    n 1: severe spasm in which the back arches and the head bends
         back and heels flex toward the back

from The Collaborative International Dictionary of English v.0.48

Opisthotonos \Op`is*thot"o*nos\, n. [NL., from Gr. ? backwards +
   ? a stretching.] (Med.)
   A tetanic spasm in which the body is bent backwards and
   stiffened.
   [1913 Webster]