The Collaborative International Dictionary of English v.0.48:

Hare's-tail \Hare's"-tail`\ (-t[=a]l`), n. (Bot.)
   A kind of grass (Eriophorum vaginatum). See Cotton grass,
   under Cotton.
   [1913 Webster]

   Hare's-tail grass (Bot.), a species of grass (Lagurus
      ovatus) whose head resembles a hare's tail.
      [1913 Webster]