Origins
The most famous margin in history belonged to Pierre de Fermat's copy of Arithmetica.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ In 1637, he wrote in the blank edge of a page that he had proved something remarkable but the margin was too narrow to contain it. That marginal note created a 358-year mathematical quest.
Latin margΕ meant 'edge, brink, border, rim'. The word likely traces to PIE *merΗ΅- ('boundary'), making it a distant relative of mark and demarcation. The earliest English use referred to the edges of manuscript pages β the blank space surrounding the text.
Medieval scholars turned margins into a parallel text. Marginalia β notes, corrections, arguments, and drawings in the margins β became a recognised intellectual tradition. Some medieval manuscripts have marginalia more valuable than the text they surround.
Development
The financial sense crystallised in the 18th century. A profit margin is the space between cost and revenue β the edge between loss and gain. Trading on margin means operating at the border of what you can afford, using borrowed money to extend beyond your actual capital.
The election sense treats the margin as a gap: the distance between winner and loser. A narrow margin means the candidates were close to the same edge.
All modern uses preserve the spatial original. Whether in publishing, finance, or politics, a margin is always the space at the boundary β the area where the main content ends and something else begins.