Английский Этимологический словарь - mortgage (n.)

- late 14c., from O.Fr. morgage, mort gaige, lit. "dead pledge," from mort "dead" + gage "pledge;" so called because the deal dies either when the debt is paid or when payment fails. O.Fr. mort is from V.L. *mortus "dead," from L. mortuus, pp. of mori "to die." The verb is first attested 1467.