Origin: 1375–1425; Middle English amortisen < Anglo-French, Old French amortiss-, long stem of amortir literally, to kill, die < Vulgar Latin *a(d)mortīre (derivative of Latin mors, stem mort- death, with ad-ad-); -ize later replacing -is(s)-, probably by association with Anglo-Latin a(d)mortizāre
late 14c., from O.Fr. amortiss-, prp. stem of amortir "deaden," from V.L. *admortire "to extinguish," from L. ad- "to" + mors (gen. mortis) "death" (see mortal). Originally a legal term for an act of alienating lands. Meaning "extinguish a debt" (in form amortization) is attested from 1864.