An archaic form of 'debel,' meaning to subdue, suppress, or overcome in war or conflict.
From Latin de- (down, against) plus bellum (war), with the double-l representing a variant spelling found in Middle English texts. This is essentially an older spelling of the same Latin-derived concept.
The variation between 'debel' and 'debell' shows you how English spelling was in flux during the medieval and early modern periods—before dictionaries locked things down, the same word could appear multiple ways in different manuscripts!
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