Lewis & Short

clāva, ae, f. [root cel- of percello; cf. Gr. κλάω and clades].

  1. I. A knotty branch or stick, a staff, cudgel, club: adfer duas clavas … probas, Plaut. Rud. 3, 5, 20; Lucr. 5, 968: sternentes agmina clavā, Verg. A. 10, 318; Curt. 9, 4, 3; Ov. F. 1, 575; Cic. Verr. 2, 4, 43, § 94; Plin. 19, 1, 3, § 18; a bar, lever, Cato, R. R. 13, 1.
    As a weapon for exercising, used by young men, and esp. by soldiers, a foil, Cic. Sen. 16, 58; Veg. Mil. 1, 11.
    As a badge of Hercules, Prop. 4 (5) 9, 39; Ov. H. 9, 117; id. M. 9, 114; 9, 236; * Suet. Ner. 53; cf. Paul. ex Fest. p. 62 Müll.
    Hence, prov., clavam Herculi extorquere, for an impossible undertaking, Macr. S. 5, 3; Don. Vit. Verg.
    Also Clava Herculis, a plant, otherwise called nymphea, Marc. Emp. 33.
  2. II. In the lang. of economy, a graft, scion, Pall. Mart. 10, 12 and 13; cf. clavula.