Wow, good timing. I just learned this one today.
Etymology of the word clue: The word clue originates with the myth of Theseus, who used a ball of yarn to find his way back out of the minotaur's labyrinth. The middle English word for a ball of yarn was clew (or clewe); when the myth was popularized in England by Chaucer, people started using the word clew figuratively to mean a hint or guide to solving a problem.