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1921, from Latin umbo "shield-boss, knob, projection."
umbo um·bo (ŭm'bō)
n. pl. um·bos or um·bo·nes (ŭm-bō'nēz)
A small anatomical projection on a surface, such as that on the inner surface of the tympanic membrane at the end of the manubrium of the malleus, corresponding to the most depressed point of the membrane.