Is the game afoot

A friend recently asked me about the term "afoot." His question was, "Could you say, 'I was on a horse and she was afoot'?" Please notice the very tricky punctuation and I think I got it right. Anyway, there were voices in the background and I could tell that a bet was on the line.

"Sure," I said. "It's kind of an old-fashioned word, and we'd probably say 'on foot' today."

After my friend hung up, I wondered what had occasioned the bet. Then I remembered a phrase attributed to Sherlock Holmes, but one he never actually uttered in one of Conan Doyle's stories. It's "The game is afoot."

A game walking? Of course not. In this case, the meaning of the word is "happening." Something is afoot.

So, what we have is a word with two meanings. Actually, it'd probably be more accurate to say that we have two different words which just happened to be spelled the same. The word "run" in "a run of good luck," is clearly connected to the original meaning of the word "run," and can be seen to be a metaphor. Sometimes, though, as with "afoot," the meanings have separated too far. Or, it might be the case that the two words "afoot" in fact come from different roots. I'll have to look that one up.