Noah Webster's New International Dictionary of the English Language

1. (n.) That which lies in the middle, or between other things; intervening body or quantity. Hence, specifically: (a) Middle place or degree; mean.

2. (n.) See Mean.

3. (n.) The mean or middle term of a syllogism; that by which the extremes are brought into connection.

4. (n.) A substance through which an effect is transmitted from one thing to another; as, air is the common medium of sound. Hence: The condition upon which any event or action occurs; necessary means of motion or action; that through or by which anything is accomplished, conveyed, or carried on; specifically, in animal magnetism, spiritualism, etc., a person through whom the action of another being is said to be manifested and transmitted.

5. (n.) An average.

6. (n.) A trade name for printing and writing paper of certain sizes. See Paper.

7. (n.) The liquid vehicle with which dry colors are ground and prepared for application.

8. (a.) Having a middle position or degree; mean; intermediate; medial; as, a horse of medium size; a decoction of medium strength.