English colonel is pronounced the same as kernel. This seems odd, but there is an explanation. In many languages when a word contains two identical or similar sounds, one of these sounds will often change over a period of time. This kind of change is called dissimilation. So when the Italian word colonello was taken into French, it became coronel; and the word was borrowed by the English from the French in this form. Later the spelling colonel came to be used in order to reflect the Italian origin of the word. But by then the pronunciation with r was well established.