*medhyo-

The core idea of this root was:

middle, in the middle

It might be a version of the root *me- which was about measuring but that’s not certain.

The original sense of middle has been preserved in the family and is still visible in many of the offspring.
Here’s an (incomplete) list:

• mid, middle, amid
• mezzo
• median, medial
• mediocre
• intermediate
• medieval
• meso-
• milieu