The question of the "thinnest" organ is ambiguous because it can refer to either the least thick or the one with the thinnest components. We'll address both interpretations.
Interpretation 1: Least Thick Organ
Determining the single thinnest organ by overall thickness is difficult as organs vary greatly in shape and size. However, considering surface area and overall thinness, the skin is a strong contender. Many sources refer to skin as the largest organ in the body. While not uniformly thin, areas like the eyelids and lips possess exceptionally thin layers. Reference: http://www.betterhealth.vic.gov.au/health/conditionsandtreatments/skin states that "the skin on our lips and eyelids is very thin and delicate".
Interpretation 2: Organ with the Thinnest Components
If we consider the thinnest components within an organ, then the lungs stand out. The capillaries in the alveoli (tiny air sacs in the lungs) are exceptionally thin, allowing efficient gas exchange. [Reference: provided text: The organ with the thinnest capillaries in the human body is the lungs. Specifically, the capillaries in the alveoli (the tiny air sacs in the lungs) are exceptionally thin, allowing for efficient gas exchange between the air in the alveoli and the blood in the capillaries. 02-Mar-2018] These capillaries are much thinner than any other blood vessel type in the body. Reference: https://my.clevelandclinic.org/health/body/21988-capillaries states that "Capillaries are the smallest blood vessels in your vascular system."
Therefore, depending on the interpretation, the answer is either the skin or the lungs.
