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.
The most important one out of a related group.
The ship occupied by the fleet's commander (usually an admiral); it denotes this by flying his flag.
The ship regarded as most important out of a group, e.g. a nation's navy or company's fleet.
To act as a flagship for.