n. That which holds a middle place or position; that which comes or stands between the extremes in a series, as of things, principles, ideas, circumstances, etc.; a mean.n. Technically— In mathematics, a mean. See mean.n. In logic, the mean or middle term of a syllogism.n. A size of paper between demy and royal. American printing-medium is 19 × 24 inches; American writing-medium, 18 × 23 inches; English printing-medium, 18 × 28 inches; English writing-medium, 17½ × 22 inches; American double medium, 24 × 38 inches; and American medium and a half, 24 × 30 inches.n. Anything which serves or acts intermediately; something by means of which an action is performed or an effect produced; an intervening agency or instrumentality: as, the atmosphere is a medium of sound.n. Specifically— In painting, any liquid vehicle, as linseed-oil, poppy-oil, varnish, or water, with which dry pigments are ground, or with which pigments are mixed by the painter while at work, in order to give them greater fluidity.n. In acoustics, a ponderable elastic substance, as air or other gas, water, etc., which transmits the energy of the sounding body in waves of condensation and rarefaction to the ear.n. In heat and light, that which transmits the energy of the heated or luminous body to a distance in undulatory waves; the ether.n. In bacteriology, the nutritive substance, either a liquid or a solid, in which or upon which the various forms of microscopic life are grown for study. The liquid media employed are infusions of hay, extract of beer-yeast, and broth of various kinds of meat. The solid media most used are eggs, slices of potatoes and carrots, agar-agar, and especially gelatin and the gelatinized serum of the blood of oxen. After being thoroughly sterilized by heat, they are usually placed in test-tubes, and inoculated with the form that it is desired to study; the cultures may then be observed through the glass.n. A person through whom, or through whose agency, another acts; specifically, one who is supposed to be controlled in speech and action by the will of another person or a disembodied being, as in animal magnetism and spiritualism; an instrument for the manifestation of another personality.n. Something of mean or medium weight, size, etc.Middle; middling; mean: as, a man of medium size.