peacefulness vs tranquillity

peacefulness and tranquillity both are nouns.

Word	Noun	Adjective	Verb	Adverb
peacefulness	Yes	No	No	No
tranquillity	Yes	No	No	No

As nouns, tranquillity is a hypernym of peacefulness; that is, tranquillity is a word with a broader meaning than peacefulness:

Other hypernyms of peacefulness include quietness, quietude, tranquility.

peacefulness (noun)	tranquillity (noun)
the absence of mental stress or anxiety	a disposition free from stress or emotion
a state that is calm and tranquil	a state of peace and quiet
	an untroubled state; free from disturbances