From WordNet (r) 3.0 (2006) [wn]:
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
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]