Anything that indicates future trends.
A stock or bond that is widely believed to be an indicator of the overall market's condition.
The leading sheep of a flock, having a bell hung round its neck.
Information which may lead one to a certain point or conclusion.
An object or a kind of indication which may be used as evidence.
Insight or understanding ("to have a clue [about]" or "to have clue". See have a clue, clue stick)
To provide with a clue.
To provide someone with information which he or she lacks (often used with "in" or "up").