- long, narrow formations of cirrus cloud somewhat like a horse's tail in shape, supposed to be a sign of changes in the wind
- the only species (Hippuris vulgaris) of an aquatic family (Hippuridaceae, order Callitrichales) of plants with tiny flowers and narrow, hairlike leaves growing in thick whorls around the slender, erect stems
See mare's-tail in American Heritage Dictionary 4
noun pl. mare's-tails
or mares'-tails (mârzˈtālzˌ)
- A cosmopolitan aquatic herb (Hippuris vulgaris) having minute flowers and linear whorled leaves.
- A long narrow cirrus cloud with a flowing appearance.