umbo

/ˈʌmboʊ/
noun
  1. A rounded, raised boss or knob at the center of a shield.
    • The museum displayed a bronze umbo from an ancient Greek shield.
    • The Viking shield had an iron umbo that protected the warrior's hand.
    • He polished the umbo until it gleamed like a mirror.
  2. The beak or pointed tip of a bivalve mollusk shell, near the hinge.
    • The clam's umbo showed growth rings like a tree trunk.
    • The fossil had a well-preserved umbo with fine ridges.
    • She identified the species by the shape of its umbo.
  3. A central, raised part of any structure; a boss or protuberance.
    • The cathedral's dome had an ornate umbo at its peak.
    • Geologists studied the umbo of the volcanic mound.
    • The fungus had a dark umbo in the center of its cap.
Antonyms