The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

colonel
    n 1: 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

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "colonel":
   ADC, CO, OD, aide, aide-de-camp, brigadier, brigadier general,
   captain, chicken colonel, chief of staff, commandant, commander,
   commander in chief, commanding officer, commissioned officer,
   company officer, exec, executive officer, field marshal,
   field officer, first lieutenant, five-star general,
   four-star general, general, general officer, generalissimo,
   jemadar, junior officer, lieutenant, lieutenant colonel,
   lieutenant general, major, major general, marechal, marshal,
   officer, one-star general, orderly officer, risaldar,
   senior officer, shavetail, sirdar, staff officer, subahdar,
   subaltern, sublieutenant, the Old Man, the brass,
   three-star general, top brass, two-star general



Bouvier's Law Dictionary, Revised 6th Ed (1856):

COLONEL. An officer in the army, next below a brigadier general, bears this
title.