Ken is a noun that refers to one’s range of knowledge.
Our word of the day has its roots in the German word kennen (KEN en) which means ‘to know’ or ‘be acquainted with.’ The word was imported into English in the 16th century, carrying its same basic meaning. Here’s an example:
That World War Two movie we saw the other day was fun, but it didn’t seem realistic. Granted, history is a little out of my ken, but even someone whose area of expertise isn’t history knows they didn’t have cell phones at Pearl Harbor.
