Diabetes mellitus or, less often, to diabetes insipidus. Diabetes mellitus and diabetes insipidus share the name “diabetes” because they are both conditions characterized by excessive urination (polyuria).

The word “diabetes” is borrowed from the Greek word meaning “a siphon.” The 2nd-century A.D. Greek physician, Aretus the Cappadocian, named the condition “diabetes.” He explained that patients with it had polyuria and “passed water like a siphon.”

When “diabetes” is used alone, it refers to diabetes mellitus. The two main types of diabetes mellitus — insulin-requiring type 1 diabetes and adult-onset type 2 diabetes — are distinct and different diseases in themselves.