Definition of umbo in English:

umbo

noun

  • 1historical The central boss of a shield.

    • ‘The nearly spherical cones have eight to 10 scales, each looking like a shield with a central projection (called an umbo, if you want to impress your botanist or Scrabble-playing friends).’
  • 2Biology
    A rounded knob or protuberance.

    lump, bump, protuberance, projection, protrusion, bulge, swelling, knot, node, nodule, gnarl, growth, outgrowth, excrescence, carbuncle, tumour
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    1. 2.1Zoology
      The highest point of each valve of a bivalve shell.
      • ‘The oldest part of the shell, the umbo, can be recognized as a large hump on the anterior end of the dorsal side of each shell.’
      • ‘The new species is characterized by a transversely extended, strongly biconvex to globular shell with prominent umbones, relatively numerous costae and a notothyrial cavity supported dorsally by a short median ridge.’
      • ‘Argonauta attaches the egg-mass to the umbo of the shell near the dorsal arms, not in the mantle cavity or posterior parts of the shell.’
      • ‘Below the umbones, the shell margin is folded inward forming a deep lunula and gaping between both valves.’
      • ‘In contrast, a strongly obtuse apical angle is associated with an incurved ventral beak that is appressed to the dorsal umbo, resulting in the delthyrium being partly obscured.’
    2. 2.2Botany
      A central swelling on the cap of a mushroom or toadstool.

Origin

Early 18th century: from Latin, shield boss.

Pronunciation:

umbo

/ˈʌmbəʊ/