mid-14c., "edge of a sea or lake;" late 14c., "space between a block of text and the edge of a page," from Latin marginem (nominative margo) "edge, brink, border, margin," from PIE *merg- "edge, border, boundary" (see mark, n.1). General sense of "boundary space; rim or edge of anything" is from late 14c. Meaning "comfort allowance, cushion" is from 1851; margin of safety first recorded 1888. Stock market sense of "sum deposited with a broker to cover risk of loss" is from 1848. Related: Margins.

c.1600, "to furnish with marginal notes," from margin, n.. From 1715 as "to furnish with a margin."