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]