bellwether

• bell-wether

From Middle English belwether, belleweder (“a sheep with a bell around its neck to lead a flock”), equivalent to bell +‎ wether.

• IPA^(key): /ˈbɛlwɛðə/ (RP)
• (US) IPA^(key): /ˈbɛlwɛðɚ/

• Audio (US)

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bellwether (plural bellwethers)

1. The leading sheep of a flock, having a bell hung round its neck.
   • 1861, Oliver Wendell Holmes, Sr., Elsie Venner, 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.

2. Anything that indicates future trends.
3. A stock or bond that is widely believed to be an indicator of the overall market's condition.

• (indicates trends): gauge, indicator, sign

• omen
• harbinger