Definition of medium:
a means or instrumentality for storing or communicating information
the surrounding environment; "fish require an aqueous medium"
an intervening substance through which signals can travel as a means for communication
(bacteriology) a nutrient substance (solid or liquid) that is used to cultivate micro-organisms
a liquid with which pigment is mixed by a painter
(biology) a substance in which specimens are preserved or displayed
an intervening substance through which something is achieved; "the dissolving medium is called a solvent"
a state that is intermediate between extremes; a middle position; "a happy medium"
someone who serves as an intermediary between the living and the dead; "he consulted several mediums"
(usually plural) transmissions that are disseminated widely to the public
an occupation for which you are especially well suited; "in law he found his true metier"
around the middle of a scale of evaluation; "an orange of average size"; "intermediate capacity"; "medium bombers"
(meat) cooked until there is just a little pink meat inside