asses' bridge

noun

: the fifth proposition of the first book of Euclid: the angles at the base of an isoceles triangle are equal to one another

a schoolboy, stammering out his asses' bridge

—Frederic Harrison

Word History

Etymology

translation of New Latin pons asinorum; probably from the similarity of the geometrical construction demonstrating it to the trusses of a bridge and from its being considered a difficulty for poor students of geometry

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