clue: [15] Clue is a variant spelling of the now obsolete clew ‘ball of thread’, and its current application to ‘that which helps to solve a problem’, which originated in the early 17th century, is based on the notion of using (like Theseus in the Minotaur’s labyrinth) a ball of thread to show one the way out of an intricate maze one has entered. Clew itself goes back to Old English cliwan or cleowan, which may be related to claw. => claw[clue etymology, clue origin, 英语词源]