A long, detailed, formal essay or piece of writing that carefully examines and discusses a subject thoroughly.
From Latin disquisitio, derived from disquirere (to inquire thoroughly), literally 'a thorough searching out'—this noun form became standard for academic works.
This word is actually alive and well in academic circles today—when scholars publish long, dense papers exploring subjects exhaustively, they're still writing 'disquisitions' even if they don't call them that!
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