A collapse or crumbling, especially of a structure, cliff, or fortification due to erosion or damage.
From French 'éboulement,' derived from 'ébouler' (to collapse), which comes from 'é-' (out) and 'boul-' (related to 'boule,' ball/mass). The term entered English geological and military vocabulary in the 19th century.
Military engineers studying old French fortifications developed this term to describe how castle walls and defensive structures would spectacularly crumble when undermined—it's basically the technical word for 'castle collapse.'
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