Definition of "ictus"

The pulse.  examples

(medicine) A sudden attack, blow, stroke, or seizure, as in a sunstroke, the sting of an insect, pulsation of an artery, etc.  examples

(prosody) The stress of voice laid upon an accented syllable of a word. Compare arsis.  examples

(music) In conducting, the indication of a musical event, most often the beat of the tempo or the entry of a section of the orchestra.  examples