Lewis & Short

umbo, ōnis, m. [kindr. with ἄμβων, ὀμφαλός, umbilicus; Germ. Nabel; Engl. navel]; prop. any convex elevation; hence,

  1. I. A boss of a shield, Enn. ap. Macr. S. 6, 3 (Ann. v. 432 Vahl.); Verg. A. 2, 546: scutis magis quam gladiis geritur res: umbonibus incussāque alā sternuntur hostes, Liv. 9, 41, 18.
    1. B. Transf., a shield (in prose not ante-Aug.; syn. clipeus), Verg. A. 7, 633; 9, 810; 10, 884; Sil. 4, 354; Liv. 4, 19, 5; 30, 34, 3; Auct. ap. Quint. 8, 5, 24: junctae umbone phalanges, Juv. 2, 46; cf. Luc. 6, 192: umbone se protegere, Just. 33, 2.
      Trop.: judicialis, Val. Max. 8, 5, 4.
  2. II. The elbow, Mart. 3, 46, 5; Stat. Th. 2, 670; Suet. Caes. 68 fin.
  3. III. A promontory, Stat. Achill. 1, 408.
    Hence, transf., Isthmius, the Isthmus of Corinth, Stat. Th. 7, 15.
  4. IV. A projecting boundary-stone in fields, Stat. Th. 6, 352.
  5. V. A projecting part of a precious stone, a knob, boss, Plin. 37, 6, 23, § 88.
  6. VI. The full part or swelling of a garment, Tert. Pall. 5.
    Hence, transf.: umbo candidus, a toga, Pers. 5, 33.