hypotenuse

From Latin hypotenusa, from Ancient Greek ὑποτείνουσα πλευρά (hupoteínousa pleurá, “side subtending [the right angle]”), from ὑποτείνουσα (hupoteínousa, “stretching, extending, subtending”), active participle of ὑποτείνω (hupoteínō, “subtend, stretch under”).

来源：wiktionary