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 The ""boss of a shield""  is called a buckle, from the Middle English ""bocle"" and the Old French ""bocle"" or ""bucle"" . The ""boss of the shield"" is the ring of the shield. Source: Webster's New Twentieth Century Dictionary of the English Language. 1943 

 The ""boss of the shield"" in Late Latin is called a ""bucula' or ""buccula"",or the beaver of a helmet from the bulging shape. Source: An Anglo-Saxon Dictionary by T. Northcote Toller (1921)cited @ lexicon.ff.cuni.cz/html/oe_bosworthtoller/d0110.html   "