"bridge," in various Latin expressions, from Latin pons "bridge, connecting gallery, walkway," earlier probably "way, passage," from PIE *pent- "to go, tread" (see find, v.). Especially pons asinorum "bridge of asses," nickname for the fifth proposition of the first book of Euclid, which beginners and slow wits find difficulty in "getting over": if two sides of a triangle are equal, the angles opposite these sides also are equal.