What is the meaning of Mare's-tail?

A long streaky cloud, spreading out like a horse's tail, and believed to indicate rain; a cirrus cloud.

Any aquatic plant of the genus Hippuris, having narrow leaves in whorls.

  1. especially, common mare's tail (Hippuris vulgaris)

especially, common mare's tail (Hippuris vulgaris)

Erigeron canadensis (syn. Conyza canadensis), an annual weed.

Equisetum, a fern ally.

Source: wiktionary.org