D defs.my
Entry 2 senses Webster, 1913

Bellwether

/bĕl'-wĕthˌ-ẽr/ · Bell·weth·er · IPA /ˈbɛlwɛðɚ/
01 n. A wether, or sheep, which leads the flock, with a bell on his neck.
  1. 1.
    A wether, or sheep, which leads the flock, with a bell on his neck.
  2. 2.
    Hence: A leader.[Contemptuous]