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n. pl. um·bo·nes (ŭm-bō′nēz) or um·bos
1. The boss or knob at the center of a shield.
a. Biology A knoblike protuberance arising from a surface, as the prominence near the hinge of a bivalve shell or the raised area in the center of the cap of a mushroom.
b. Anatomy A small projection at the center of the outer surface of the eardrum.

[Latin umbō, umbōn-; see nobh- in Indo-European roots.]

um′bo·nal (ŭm′bə-nəl, ŭm-bō′nəl) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


n, pl umbones (ʌmˈbəʊniːz) or umbos
1. (Botany) a small hump projecting from the centre of the cap in certain mushrooms
2. (Zoology) a hooked prominence occurring at the apex of each half of the shell of a bivalve mollusc
3. (Anatomy) anatomy the slightly convex area at the centre of the outer surface of the eardrum, where the malleus is attached on the internal surface
4. (Arms & Armour (excluding Firearms)) a large projecting central boss on a shield, esp on a Saxon shield
[C18: from Latin: boss of a shield, projecting piece]
umbonate, umbonal, umbonic adj
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˈʌm boʊ)

n., pl. um•bo•nes (ʌmˈboʊ niz) um•bos.
1. a boss on a shield.
2. any similar boss or protuberance.
3. the beak of a bivalve shell; the protuberance of each valve above the hinge.
4. the raised area on the inner surface of the tympanic membrane, where the malleus is attached.
[1715–25; < Latin umbō; akin to umbilīcus (see umbilicus)]
um′bo•nal (-bə nl) adj.
um′bo•nate (-nɪt, -ˌneɪt) adj.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.umbo - a slight rounded elevation where the malleus attaches to the eardrumumbo - a slight rounded elevation where the malleus attaches to the eardrum
eardrum, myringa, tympanic membrane, tympanum - the membrane in the ear that vibrates to sound
convex shape, convexity - a shape that curves or bulges outward
Based on WordNet 3.0, Farlex clipart collection. © 2003-2012 Princeton University, Farlex Inc.
References in periodicals archive ?
The primary layer has not been found but longitudinal rows of vertical fine crystals, possibly altered remains of original capillae, are observed on the umbonal region of one ventral valve (Fig.
mamillatus was characterized by the thick wall, narrowly spaced chambers and the presence of umbonal pillars as seen in the vertical view.
Boreholes were found most often in region 1 of bivalves, with 68%, 100%, and 74% of boreholes found near the umbo for Mya arenaria, Spisula solidissima, and Tellina carpenteri, respectively; however, no umbonal preference was evident for Gemma gemma.
Concha pequena, delgada, inflada, con borde anterior redondeado y el lado posterior prolongado para formar un largo rostrum cuyo borde dorsal es ligeramente concavo y bicarinado en cada valva, el espacio entre las carinas presenta, cuerdas concentricas; el area umbonal lleva varias cuerdas concentricas notorias y en el resto del disco hay finas estrias concentricas; charnela taxodonta con 18 dientes anteriores y 30 posteriores; el ligamento se inserta oblicuamente en suaves depresiones del condroforo, el cual es una lamina situada bajo los umbos.
For the shell studies, a digital calliper was used and the following measures were taken: length (greater distance between the anterior and the posterior axis of the shell), height (distance between the ventral and dorsal axis of the shell, passing through the umbonal region), width (distance between the two valves, with the shell closed, also passing through the umbonal region) and length of the ligament.
Although Mongin (1961: 341) did not mention any umbonal ornamentation on English specimens, we did observe it on some specimens.
The umbonal area is smooth but the ventral and posterior portions of the valve bear relatively coarse, closely-spaced costae radiating from the direction of the beak.
Both species possess comparable beak placement, the number of umbonal corrugations that curve ventrad around the umbo, disc convexity, and node shape, node prominence, and number of nodes.