mercyyoudaoicibaDictYouDict[mercy 词源字典]
mercy: [12] Latin mercēs meant ‘payment, reward’. In the Christian era the notion of a ‘reward’ was taken up and reapplied metaphorically to the ‘compassion given freely by God to humankind’, and the word passed into Old French (in the form merci) with the broader sense ‘compassion’, and hence ‘forbearance from punishment’. English took it over and has continued to use it in much the same way, but its main role in modern French is as the word for ‘thank you’.
[mercy etymology, mercy origin, 英语词源]
mercy (n.)youdaoicibaDictYouDict
late 12c., "God's forgiveness of his creatures' offenses," from Old French mercit, merci (9c.) "reward, gift; kindness, grace, pity," from Latin mercedem (nominative merces) "reward, wages, pay hire" (in Vulgar Latin "favor, pity"), from merx (genitive mercis) "wares, merchandise" (see market (n.)). In Church Latin (6c.) applied to the heavenly reward of those who show kindness to the helpless.

Meaning "disposition to forgive or show compassion" is attested from early 13c. As an interjection, attested from mid-13c. In French largely superseded by miséricorde except as a word of thanks. Seat of mercy "golden covering of the Ark of the Covenant" (1530) is Tyndale's loan-translation of Luther's gnadenstuhl, an inexact rendering of Hebrew kapporeth, literally "propitiatory."