Definitions of medium:

• noun:   an intervening substance through which signals can travel as a means for communication
• noun:   a means or instrumentality for storing or communicating information
• noun:   transmissions that are disseminated widely to the public
• noun:   the surrounding environment

  Example: "Fish require an aqueous medium"

• noun:   someone who serves as an intermediary between the living and the dead

  Example: "He consulted several mediums"

• noun:   a state that is intermediate between extremes; a middle position

  Example: "A happy medium"

• noun:   an intervening substance through which something is achieved

  Example: "The dissolving medium is called a solvent"

• noun:   (biology) a substance in which specimens are preserved or displayed
• noun:   a liquid with which pigment is mixed by a painter
• noun:   an occupation for which you are especially well suited
• noun:   (bacteriology) a nutrient substance (solid or liquid) that is used to cultivate micro-organisms
• adjective:   (of meat) cooked until there is just a little pink meat inside
• adjective:   around the middle of a scale of evaluation of physical measures

  Example: "Medium bombers"