mare's-tail

Noun

 * 1) A long streaky cloud, spreading out like a horse's tail, and believed to indicate rain; a cirrus cloud.
 * 2) Any aquatic plant of the genus Hippuris, having narrow leaves in whorls.
 * 3) especially,
 * 4)  (syn. ), an annual weed
 * , a fern ally
 * , a fern ally