Which of the following describes a yellowish discoloration of the skin due to increased bilirubin levels in the blood?

The term that accurately describes a yellowish discoloration of the skin resulting from elevated bilirubin levels in the blood is "icterus." This condition is commonly associated with liver dysfunction, where the liver fails to adequately process bilirubin, leading to its accumulation in the bloodstream. Consequently, bilirubin deposits in tissues, especially in the skin and sclera (the whites of the eyes), causing the characteristic yellow hue.

In medical terminology, icterus is often used interchangeably with jaundice, which is the clinical manifestation of the underlying problem of bilirubin metabolism. The other terms listed do not relate to this specific symptom: diarrhea refers to frequent loose or watery bowel movements, achalasia is a disorder of the esophagus affecting its ability to move food into the stomach, and diverticular disease pertains to the formation of diverticula in the colon, which can lead to complications but does not cause yellowish discoloration of the skin. Therefore, "icterus" is the correct choice in this context.