Why is colonel pronounced with an R and TWO syllables instead of an L and three syllables?
At the time, I had no idea. I've since done some digging (thank you, OED and Professor Google, but mostly OED), and now I have an answer for people as nerdy as I am (ie anyone who loves weird language stuff).
First (of course), some history.
The term for the military rank we know as colonel comes from the commander of the regiment of the "little column," or the first company of a regiment. The French and Italian armies used their words for column, colonna and colonello/colonella, and the English adopted similar terms.
So at that point, army folks did use the L-sound when referring to the rank.
Thanks to something called dissimilation, some sounds change in words over time. (Remember how P changed to F in many old words like pater --- father and pisk --- fish?)
Same thing happened with R changing to L. For example, the French word marbre underwent dissimilation with the last R and became the English marble.
Moving back to colonel.
Because of dissimilation, the middle L in colonel took on the sound of R for some people. The English used both colonel (a word with THREE syllables and an L-sound) and coronel interchangeably for quite some time.
The distinction between R and L in some words didn't matter; both were used in this case and accepted as correct.
It wasn't until after 1650 that the spelling of coronel finally lost popularity in the written word, in favor of colonel. But both pronunciations (both L and R, with 3 syllables to the word) were still used verbally. COL-o-nel and COR-o-nel.
By the end of that century (again, as is typical in language), the word was often shortened in speech to two syllables, but still with the L-sound.
So we had:
KUL-nel instead of KUL-o-nel
KER-nel instead of KER-o-nel).
By 1816, three things had happened:
- the two-syllable version had taken over as the favorite KUL-nel/KER-nel
- the spelling was standardized with the L (No more coronel. Just colonel.)
- the pronunciation stuck with the dissimilated R.
Tada! Today we have COLONEL pronounced as KER-nul.
(I don't remember who first asked, but thanks for the question!)