@McTag,
Interesting, I agree, McTag, but I don't believe that it is all that helpful to any learner of the language. All the illustrious folk here knew the meaning and how to use it but none really knew the origins of the word.
Let's just imagine for a moment that the origin of the idiom, 'at bay', is the one proffered by Ionus. That doesn't change how we use it in the English of today, nor does it in any way affect its current meaning.