quietus (n.)

"discharge, clearing of accounts," 1530s, short for Medieval Latin phrase quietus est "he is quit," from quietus "free" (in Medieval Latin "free from war, debts, etc."), also "calm, resting" (from PIE root *kweie- "to rest, be quiet"). Hence, "death" (i.e. "final discharge"), c. 1600. Latin quies also was used for "the peace of death."