mortality (n.)

mid-14c., "condition of being mortal," from Old French mortalite "massacre, slaughter; fatal illness; poverty; destruction" (12c.), from Latin mortalitem (nominative mortalitas) "state of being mortal; subjection to death," from mortalis "subject to death, mortal," from PIE root *mer- "to rub away, harm" (also "to die" and forming words referring to death and to beings subject to death). Meaning "widespread death" is from c. 1400; meaning "number of deaths from some cause or in a given period" is from 1640s.