The intelligent person or people in a group: the director, planner, administrator, etc.
The substance of a brain, as a material or foodstuff.
The figurative substance of a brain: mental ability, intelligence.
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.