Source : Webster's Revised Unabridged Dictionary (1913)

Colonel \Colo"nel\, n. [F. colonel, It. colonello, prop., the
   chief or commander of a column, fr. colonna column, L.
   columna. See {Column}.] (Mil.)
   The chief officer of a regiment; an officer ranking next
   above a lieutenant colonel and next below a brigadier
   general.

Source : WordNet®

colonel
     n : a commissioned military officer in the United States Army or
         Air Force or Marines who ranks above a lieutenant colonel
         and below a brigadier general