What is the correct combining form for vessel?

The correct combining form for "vessel" is vas/o. This form is derived from the Latin word "vas," which means "vessel" and is commonly used in medical terminology. For example, terms like "vasculitis" (inflammation of blood vessels) and "angioplasty" (a procedure to widen narrowed or obstructed blood vessels) utilize this combining form.

In contrast, the other options represent different medical terms. The combining form psych/o pertains to the mind or mental processes, used in terms like "psychology." Proct/o relates to the rectum and anus, seen in words like "proctology." Path/o is associated with disease and suffering, used in terms like "pathology." Each of these forms has its own specific set of applications in medical language, but vas/o is uniquely identified with vessels, particularly in relation to blood vessels or other types of tubular structures in the body.