requiem (n.)

"mass for repose of the soul of the dead," c. 1300, from Latin requiem, accusative singular of requies "rest (after labor), repose," from re-, intensive prefix (see re-), + quies "quiet" (from suffixed form of PIE root *kweie- "to rest, be quiet"). It is the first word of the Mass for the Dead in the Latin liturgy: Requiem æternam dona eis, Domine .... ["Grant them eternal rest, O Lord ...."]