What is the meaning of Horsetail?

The tail of a horse. (Can we add an example for this sense?)

Any of various simple vascular plants, of the order Equisetales, that have hollow stems and produce spores.

A Turkish standard denoting rank.

A mare's tail, a water plant in genus Hippuris.

Any waterfall, the descending water of which maintains contact with bedrock most of the time.

cauda equina, a bundle of nerve fibers.

A ponytail hairstyle.

Source: wiktionary.org