A “clue” used to be a ball of thread

Follow a clue far enough and you end up in a Greek labyrinth. The word is literally the thread that led Theseus back out.

Before a clue was a hint, it was a thing you could hold: a clew, an old word for a ball of thread. Same word, older spelling. The ue version didn't take over until around the 1600s.

So how did a ball of yarn become the thing a detective chases? Blame a labyrinth.

The etymology of “clue”

In the Greek myth, Theseus goes into the Minotaur's maze to kill it, but nobody walks out of that maze. Ariadne hands him a ball of thread and tells him to unwind it on the way in. Kill the monster, then follow the thread back to the door.

That ball of thread was a clew. The idea stuck so hard that by the 1600s people were using it for anything that guides you through a confusing problem, a fact that unwinds toward the answer. The literal thread faded; the metaphor stayed.

Which means every detective "following a clue" is doing exactly what Theseus did — feeling along a thread through the dark, hoping it leads somewhere out.