Clue, n.
[See CLEW.] 1. A ball of thread; thread wound into a ball.
You have wound a goodly clue. Shak.
Sense 2. Thread unwound from a ball, used to guide a person in a labyrinth.
Sense 3. Any thing serving to guide or direct. “Discoveries and observations that . . . [do not] serve as clues to guide us into further knowledge.” Locke.
Sense 4. (Naut.) One of the two lower corners of a square-sail.