The word colonel was derived from the Italian word “colonnello” means column of soldiers, rooted from the Latin “colonna” means column. The word appeared some time around early 1500s.
In translation from Italian to French, the word got corrupted from colonello to coronel. The British took the word from the French and then later slurred down to “kernel”, but using the same spelling “coronel”.
By the end of the 16th Century, scholars changed the spelling back to its Italian origin. But they ran into a problem because at the time, most poor people were illiterate. They had learned the word orally, and didn’t know that the spelling of the word had changed.
After a while, they gave up and decided that the word would be spelled “colonel” but that the proper pronunciation would be “kernel.”
And here’s the twist, not all Americans pronounce the word colonel as “kernel” or “kernul”, some don’t pronounce the “r”. I guess the English language had gone too far with this borrowed word. 😀