Colonel
mid 16th century: from obsolete French coronel (earlier form of colonel ), from Italian colonnello ‘column of soldiers’, from colonna ‘column’, from Latin columna . The form coronel, source of the modern pronunciation, was usual until the mid 17th century.
wiktionary
First attested 1548, from Middle French coronnel, from Old Italian colonnello(“the officer of a small company of soldiers (column) that marched at the head of a regiment”), from compagna colonnella(“little column company”), from Latin columna(“pillar”), originally a collateral form of columen, contraction culmen(“a pillar, top, crown, summit”), o-grade form from a Proto-Indo-European *kelH-(“to rise, be elevated, be prominent”). See hill, holm.
etymonline
colonel (n.)
"chief commander of a regiment of troops," 1540s, coronell, from French coronel (16c.), modified by dissimilation from Italian colonnella "commander of the column of soldiers at the head of a regiment," from compagna colonella "little column company," from Latin columna "pillar," collateral form of columen "top, summit" (from PIE root *kel- (2) "to be prominent; hill").
The French spelling was reformed late 16c. English spelling was modified 1580s in learned writing to conform with the Italian form (via translations of Italian military manuals), and pronunciations with "r" and "l" coexisted until c. 1650, but the earlier pronunciation prevailed. Spanish and Portuguese coronel, from Italian, show similar evolution by dissimilation and perhaps by influence of corona. Abbreviation col. is attested by 1707.
