Horsetail \Horse"tail`\, n. 1. (Bot.) A leafless plant, with hollow and rushlike stems. It is of the genus {Equisetum}, and is allied to the ferns. See Illust. of {Equisetum}. 2. A Turkish standard, denoting rank. Note: Commanders are distinguished by the number of horsetails carried before them. Thus, the sultan has seven, the grand vizier five, and the pashas three, two, or one. {Shrubby horsetail}. (Bot.) See {Joint-fir}.