E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
I have not yet got the clue to give a clue, i.e. a hint. A clue is a ball of thread (Ang.-Saxon, cleowen). The only mode of finding the way out of the Cretan labyrinth was by a skein of thread, which, being laid along the proper route, indicated the right path.