qui·e·tus 
(kwī-ētəs)
(kwī-ētəs)n.
1. Something that serves to suppress, check, or eliminate: "He was blindsided by a conflict in Korea that put the quietus on his China venture" (Robert L. Beisner).
2. Release from life; death.
3. A final discharge, as of a duty or debt.
[Short for Middle English quietus (est), (he is) discharged (of an obligation), from Medieval Latin quiētus (est), from Latin, (he is) at rest; see QUIET.]