Latin columna became Italian colonna. Its diminutive colonnello named a column of soldiers and a colonel. Middle French carried the word toward earlier English coronel.
Middle French mediation is compressed between Italian and earlier English.
Sources
- Merriam-Webster: colonel
Latin columna precedes Italian colonna and its diminutive colonnello, then earlier English coronel and modern colonel; French mediation is compressed.
- Online Etymology Dictionary · colonel
Meanings of the older forms on the word path.