Why “clue” used to be a ball of yarn

Before it meant evidence, a clue was a physical thread — the one Theseus unwound through the labyrinth so he could find the way back out.

What everyone sees

A word for a fragment of evidence, apparently unrelated to anything physical.

What is actually happening

Middle English clewe meant a ball of thread or yarn. In the myth, Ariadne gives Theseus such a ball to unwind on his way into the labyrinth so that he can retrace his path after killing the Minotaur. The story was retold so often in English that the thread became the standard image for any trail that leads out of confusion, and by the seventeenth century “clue” had drifted from the object to the guidance itself.

Why it stays hidden

Because the metaphor is so complete it stopped being one. Detectives still “follow a thread”, “unravel” a case and reach a “denouement” — French for untying — all of it left over from a ball of yarn in a maze.