Source : Webster's Revised Unabridged Dictionary (1913)

Potassoxyl \Pot`ass*ox"yl\, n. [Potassium + oxygen + -yl.]
   (Chem.)
   The radical {KO}, derived from, and supposed to exist in,
   potassium hydroxide and other compounds.

Source : WordNet®

KO
     n : a blow that renders the opponent unconscious [syn: {knockout}]