mortgage (n.)youdaoicibaDictYouDict[mortgage 词源字典]
late 14c., morgage, "conveyance of property as security for a loan or agreement," from Old French morgage (13c.), mort gaige, literally "dead pledge" (replaced in modern Frech by hypothèque), from mort "dead" (see mortal (adj.)) + gage "pledge" (see wage (n.)). So called because the deal dies either when the debt is paid or when payment fails. Old French mort is from Vulgar Latin *mortus "dead," from Latin mortuus, past participle of mori "to die" (see mortal (adj.)). The -t- restored in English based on Latin.[mortgage etymology, mortgage origin, 英语词源]