serenity vs quietude

serenity and quietude both are nouns.

Word	Noun	Adjective	Verb	Adverb
serenity	Yes	No	No	No
quietude	Yes	No	No	No

As nouns, quietude is a hypernym of serenity; that is, quietude is a word with a broader meaning than serenity:

Other hypernyms of serenity include quietness, tranquility, tranquillity.

serenity (noun)	quietude (noun)
a disposition free from stress or emotion	a state of peace and quiet
the absence of mental stress or anxiety