Bellwether

A leader, pace or trendsetter as in a bellwether stock, which is usually a blue-chip stock definitive of its industry sector. Bellwether dates originally from the 1400s, when it referred to a sheep with a bell that would lead the flock. Derives from bell + wether, where a wether is a castrated ram. It was used in its figurative sense contemptuously for centuries and it was only in the 20th century that it became fashionable as a description for blue chip stocks etc.