1.the intervening substance through which sensory impressions are conveyed or physical forces are transmitted.
2..an agency or means of doing something.
3.halfway between two extremes of size, amount, length, etc.; average.
Sooner or later visitors usually ask me which is my favourite medium. I'm guessing that they're asking about paint, not spiritual channeling :). But , hang on a minute - "medium": has quite a few meanings...especially for a painter.
The first is probably the most obvious- watercolour. oil, acrylic , pastel , ink etc etc - the chosen tool for the task.
The second - a painter is the "go between " for subject and viewer- we are putting down on paper our reaction to something , it won't (usually) be photographic. It may not even be realistic.There may be elements of artistic license.There will be personal choices made about colour, size, tone,composition.
We also sometimes use "mediums" to change the way the paint behaves - Liquin, turps or linseed oil with oil paint , oxgall or water with watercolour, and numerous acrylic mediums for all kinds of painting. These act as a go between for painter and paint.
And then we have the "average" medium - as in steak? Hopefully I don't fall into that category ,though it can sometimes be tempting to go for the safe option. But maybe medium doesn't mean the same as mediocre.
PS. and if I was forced to choose , it would probably be watercolour :)