sleep vs quietus

sleep and quietus both are nouns.

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

As nouns, sleep and quietus are synonyms defined as:

sleep and quietus: euphemisms for death (based on an analogy between lying in a bed and in a tomb)

Other synonyms of sleep include eternal rest, eternal sleep, rest.

sleep (noun)	quietus (noun)
a natural and periodic state of rest during which consciousness of the world is suspended	euphemisms for death (based on an analogy between lying in a bed and in a tomb)
euphemisms for death (based on an analogy between lying in a bed and in a tomb)
a torpid state resembling deep sleep
a period of time spent sleeping

sleep (verb)	quietus (verb)
be asleep
be able to accommodate for sleeping