Origin story
From clew, a ball of thread; later tied to the thread Ariadne gave Theseus in the labyrinth.
Why it sticks
A clue is still a thread that gets you out of a maze.
Mystery
Clue
A clue is still a thread that gets you out of a maze.
Quick answer
A short etymology card for clue: origin, meaning history, memorable hook, and source-language context.