median; midline
Geometry term for a line segment joining a vertex of a triangle to the midpoint of the opposite side, or more generally a line that divides something into two equal halves.
A median of a triangle is a line segment joining a vertex to the midpoint of the opposite side.
Please draw the midline of this figure.
Compound of 中 (middle) and 線 (line), directly describing a line that goes through the middle. The exact historical derivation is uncertain, but the term is a straightforward technical coinage.