medial (adj.)

1560s, "pertaining to a mathematical mean," from Late Latin medialis "of the middle," from Latin medius "in the middle, between; from the middle," as a noun (medium) "the middle;" from PIE root *medhyo- "middle." Meaning "occupying a middle position" is attested from 1721.

medial (n.)

"a medial letter," 1776, from medial (adj.).