Polydipsia

n. excessive thirst

Polydipsia is a medical condition in which the patient ingests abnormally large amounts of fluids by mouth. The word is made from the words poly meaning many and dipsia which means thirst. The fluid is usually water, though some people may think of alcohol because of the etymologically related term dipsomaniac, meaning an alcoholic.
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Polydipsia /poly·dip·sia/ chronic excessive thirst and fluid intake. pol·y·dip·si·a n. Excessive or abnormal thirst. pol y·dip sic adj. [more]Polydipsia - Community and Resources

Noun
1. excessive thirst (as in cases of diabetes or kidney dysfunction)
(hypernym) thirst
(part-holonym) diabetes

(n.)
Excessive and constant thirst occasioned by disease.