Definition of umbo in English:


Line breaks: umbo
Pronunciation: /ˈʌmbəʊ

noun (plural umbones /-ˈbəʊniːz/ or umbos)

1 historical The central boss of a shield.
More example sentences
  • 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).
2 Biology A rounded knob or protuberance.
2.1 Zoology The highest point of each valve of a bivalve shell.
More example sentences
  • 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.
2.2 Botany A central swelling on the cap of a mushroom or toadstool.


early 18th century: from Latin, 'shield boss'.



adjective (chiefly Zoology )
More example sentences
  • Cyzicus having elongate valves; umbo convex; dorsal margin straight; posterior margin slightly flared; growth bands widely spaced in umbonal region, more closely spaced elsewhere.
  • The umbonal angle narrows while the shape remains mytiliform and the ‘lunule’ (byssal invagination) remains shallow.
  • Hinge articulation either limited to overlapping shell margins on dorsal side of byssal invagination or consisting of a transposable tooth and socket developed on the umbonal septum.


adjective (chiefly Botany )
More example sentences
  • M. oreades has a white spore print, adnate, adnexed or even free gills usually white to pale tan in colour, a mid-sized bell-shaped cap but can later become umbonate as it ages.
  • Other decorative British products of this period include ‘umbonate’ disc brooches.
  • An umbonate colony is elevated more in the center of the colony than the rise across the surface of the colony.

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