death vs quietus

death and quietus both are nouns.

Word	Noun	Adjective	Verb	Adverb
death	Yes	No	No	No
quietus	Yes	No	No	No

As nouns, quietus is a hyponym of death; that is, quietus is a word with a more specific, narrower meaning than death:

death: the absence of life or state of being dead
quietus: euphemisms for death (based on an analogy between lying in a bed and in a tomb)

death (noun)	quietus (noun)
the act of killing	euphemisms for death (based on an analogy between lying in a bed and in a tomb)
the event of dying or departure from life
the permanent end of all life functions in an organism or part of an organism
the absence of life or state of being dead
a final state
the time when something ends
the time at which life ends; continuing until dead