Hamlet
SARAH: Quietus is short for the Latin phrase quietus est, which literally means, "he is quiet." But in classical Latin, the phrase also meant, "he is discharged of his debt, he is paid up". Throughout the medieval period, if you wrote "quietus est" on an account, it meant that the account had been paid.
RALPH: So, when Shakespeare writes, "when he himself might his quietus make", he means settling one's debt to God. Since God lends us our life, we can only settle that debt by ending our life, and returning what we've borrowed.
SARAH: So in this line, Hamlet is saying that we can settle our accounts with God by using a dagger — in other words, by dying.
RALPH: In modern English, quietus means death, but it only means this today because of this line in Hamlet. Similarly, the expression "to give or put the quietus" has come to mean to put an end to something.