diabetes insipidus

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A chronic metabolic disorder characterized by intense thirst and excessive urination, caused by a deficiency of the pituitary hormone vasopressin.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A disease characterized by excretion of large amount of severely diluted urine, which cannot be reduced when fluid intake is reduced. It is generally related to a tumor or insult to the pituitary gland, where the hormonal signals the pituitary gives to the kidneys break down, and the kidneys do not conserve water, but express all water as urine. This is a rather rare disease.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a rare form of diabetes resulting from a deficiency of vasopressin (the pituitary hormone that regulates the kidneys); characterized by the chronic excretion of large amounts of pale dilute urine which results in dehydration and extreme thirst