Why is the ninth month called September?
1560s, "pertaining to a mathematical mean," from Late Latin medialis "of the middle," from Latin medius "in the middle," from PIE *medhyo- "middle" (cf. Sanskrit madhyah, Avestan madiya- "middle," Greek mesos, Gothic midjis, Old English midd "middle," Old Church Slavonic medzu "between," Armenian mej "middle"); perhaps related to PIE root *me- "between." Meaning "occupying a middle position" is attested from 1721.
"a medial letter," 1776, from medial (adj.).
medial me·di·al (mē'dē-əl)
Relating to, situated in, or extending toward the middle; median.
Being or relating to an average or a mean.