me·di·um

– noun
1. a middle state or condition; mean.
2. something intermediate in nature or degree.
3. an intervening substance, as air, through which a force acts or an effect is produced.
4. the element that is the natural habitat of an organism.
5. surrounding objects, conditions, or influences; environment.
6. an intervening agency, means, or instrument by which something is conveyed or accomplished.
7. one of the means or channels of general communication, information, or entertainment in society, as newspapers, radio, or television.
8. the substance in which specimens are displayed or preserved.
9. a person through whom the spirits of the dead are alleged to be able to contact the living.
10. a. a liquid with which pigments are mixed.
b. the material or technique with which an artist works.