mortgage (n.)

late 14c., "deadly, destructive to life; causing or threatening death" (of illness, poisons, wounds, etc.); also, of persons or the body, "doomed to die, subject to death;" from Old French mortel "destined to die; deserving of death" and directly from Latin mortalis "subject to death, mortal, of a mortal, human," from mors (genitive mortis) "death."

This is reconstructed to be from PIE *mr-o- "to die," *mr-to- "dead," *mr-ti- "death," all from PIE root *mer- "to rub away, harm" (also "to die" and forming words referring to death and to beings subject to death). The most widespread Indo-European root for "to die," it forms the common word for it except in Greek and Germanic.

"Subject to death," hence "human, of or pertaining to humans" (early 15c.). Also from late 14c. as "implacable, to be satisfied only by death" (of hatreds, enemies, etc.). Meaning "extreme, very great" is from late 14c. A mortal sin (early 15c., opposed to venial) is one that incurs the penalty of spiritual death.

c. 1300, "a payment for services rendered, reward, just deserts;" mid-14c., "salary paid to a provider of service," from Anglo-French and Old North French wage (Old French gage) "pledge, pay, reward," from Frankish *wadja- or another Germanic source (compare Old English wedd "pledge, agreement, covenant," Gothic wadi "pledge"), from Proto-Germanic *wadi- (see wed (v.)).

Also from mid-14c., "a pledge, guarantee, surety" (usually in plural), and (c. 1400) "a promise or pledge to meet in battle." The "payment for service" sense by late 14c. extended to allotments of money paid at regular intervals for continuous or repeated service. Traditionally in English wages were payment for manual or mechanical labor and somewhat distinguished from salary or fee. Modern French cognate gages (plural) means "wages of a domestic," one of a range of French "pay" words distinguished by class, such as traitement (university professor), paye, salaire (workman), solde (soldier), récompense, prix. The Old English word was lean, related to loan and representing the usual Germanic word (Gothic laun, Dutch loon, German Lohn). Wage-earner attested from 1871.