The Collaborative International Dictionary of English v.0.48:

Ictus \Ic"tus\, n. [L., fr. icere, ictum, to strike.]
   1. (Pros.) The stress of voice laid upon accented syllable of
      a word. Cf. Arsis.
      [1913 Webster]

   2. (Med.) A stroke or blow, as in a sunstroke, the sting of
      an insect, pulsation of an artery, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ictus
    n 1: a sudden occurrence (or recurrence) of a disease; "he
         suffered an epileptic seizure" [syn: seizure, ictus,
         raptus]