The Collaborative International Dictionary of English v.0.48:

Occision \Oc*ci"sion\, n. [L. occisio, fr. occidere, occisium,
   to cut down, to kill; ob (see Ob-) + caedere to cut.]
   A killing; the act of killing. [Obs.] --Sir M. Hale.
   [1913 Webster]