Word Origin & History
51st Psalm (one of the Penitential Psalms), 13c., from Miserere mei Deus "Have mercy upon me, O God," opening line, from L. miserere "have mercy," imperative of misereri "to have mercy," from miser. From 15c.-17c. used as an informal measure of time, "the time it takes to recite the Miserere." Also in
miserere mei "kind of severe colic ('iliac passion') accompanied by excruciating cramps and vomiting of excrement" (1611).