medical name of two different affections, both characterized by abnormal discharge of urine, 1560s, from medical Latin diabetes, from late Greek diabetes "excessive discharge of urine" (so named by Aretaeus the Cappadocian, physician of Alexandria, 2c.), literally "a passer-through, siphon," from diabainein "to pass through," from dia "through" (see dia-) + bainein "to go, walk, step," from PIE root *gwa- "to go, come."
Now usually restricted to diabetes mellitus, which is characterized by an excessive quantity of sugar in the urine. An old common native name for it was pissing evil. In classical Greek, diabainein meant "to stand or walk with the legs apart," and diabetes meant "a drafting compass," from the position of the legs.