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1540s, coronell, from Middle French coronel (16c.), modified by dissimilation from Italian colonnella "commander of a column of soldiers at the head of a regiment," from compagna colonella "little column company," from Latin columna "pillar" (see hill). English spelling modified 1580s in learned writing to conform with the Italian form (via translations of Italian military manuals), and pronunciations with "r" and "l" coexisted 17c.-18c., but the earlier pronunciation prevailed. Spanish coronel, from Italian, shows a similar evolution by dissimilation.
the highest field-grade officer, ranking just below the general officer grades in most armies or below brigadier in the British services. A colonel was traditionally the commanding officer of a regiment or brigade. In air forces that use the same titles of rank as the army, such as the U.S. Air Force, a colonel's command is usually a group; the comparable grade in the Royal Air Force is group captain. When not exercising command of a regiment, group, or equivalent formation, a colonel is generally placed in a senior staff or administrative post