Dictionary of Medieval Names
from European Sources

Mercy f. Anglo-Norman merci(e), Old French merci 'mercy, grace, favor'.

This virtue name came into use in England in the 16th C (not the 17th C as Withycombe s.n. Mercy suggests).

England
Early Modern English
1560 Mercie OrpingtonKe p. 1; 1591 Mercy CAmar-vol1 p. 4
Cite as: S.L. Uckelman. "Mercy". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2016, no. 4. http://dmnes.org/2016/4/name/Mercy.