An Etymological Dictionary of Astronomy and Astrophysics

A border between two countries.
A line of division between different or opposed things.
The farthermost limits of knowledge or achievement in a particular subject.

Etymology (EN): From O.Fr. fronter, from front “forehead, brow,” → front.

Etymology (PE): Marz, from Mid.Pers. marz “boundary;” Av. marəza- “border, district,” marəz- “to rub, wipe;” Mod.Pers. parmâs “contact, touching” (→ contact), mâl-, mâlidan “to rub;” PIE base *merg- “boundary, border;” cf. L. margo “edge” (Fr. marge “margin”); P.Gmc. *marko;
Ger. Mark; E. mark, margin.