Something, such as an intermediate course of action, that occupies a position or represents a condition midway between extremes: A medium is the mean or middle term of deductive reasoning, or a syllogism, in which the opposites or extremes are brought into a context with each other.

A substance used in radiography to enhance the visibility of structures within the body: Contrast media are X-ray dyes used to provide contrast; for example, between blood vessels and other tissues.