Webster's Revised Unabridged Dictionary · 1913

Clue

Clue (klū) , noun

[See Clew, n.]

A ball of thread; a thread or other means of guidance. Same as Clew.
You have wound a goodly clue. — Shakespeare
This clue once found unravels all the rest. — Pope
Serve as clues to guide us into further knowledge. — Locke