Entry 1 sense Webster, 1913 Hare's-tail /(-tāl`)/ · Hare's·-tail · IPA 01 n. A kind of grass (Eriophorum vaginatum). See Cotton grass, under Cotton. 1. A kind of grass (Eriophorum vaginatum). See Cotton grass, under Cotton.(Bot.) See: Cotton Phrases & compounds Hare's-tail grass — a species of grass (Lagurus ovatus) whose head resembles a hare's tail.