Lewis & Short

ĕquĭsaetum, i, n. [equus-seta], the plant horse-tail, equisetum arvense, Linn., Plin. 26, 13, 83, § 132; also called ĕquĭsae-tis, is, f., id. 18, 28, 67, § 259; and ĕquĭ-sēta, ae, f., App. Herb. 40, no. 1 al.