Noun

(en noun)

The leading units at the front of an army or fleet.

(by extension) The person(s) at the forefront of any group or movement.

* {{quote-book, year=1922, author=(Ben Travers), title=(A Cuckoo in the Nest)

, chapter=4 citation , passage=By some paradoxical evolution rancour and intolerance have been established in the vanguard of primitive Christianity. Mrs. Spoker, in common with many of the stricter disciples of righteousness, was as inclement in demeanour as she was cadaverous in aspect.}}

* '>citation

Noun

(en noun)

The leading sheep of a flock, having a bell hung round its neck.

* 1861 , , chapter XXXI:

Several old ladies forthwith proclaimed their intention of following him; but, as one or two of them were deaf, and another had been threatened with an attack of that mild, but obstinate complaint, dementia senilis, many thought it was not so much the force of his arguments as a kind of tendency to jump as the bellwether jumps, well known in flocks not included in the Christian fold.

Anything that indicates future trends.

A stock or bond that is widely believed to be an indicator of the overall market's condition.