The lower corner(s) of a sail to which a sheet is attached for trimming the sail (adjusting its position relative to the wind); the metal loop or cringle in the corner of the sail, to which the sheet is attached. On a triangular sail, the clew is the trailing corner relative to the wind direction
Yarn or thread as used to guide one's way through a maze or labyrinth; a guide, a clue
Not often did Jesse James leave a clew to his identity when he galloped away from a crime of violence, back into the mysterious Nowhere whence he came.