quietude vs relaxation

quietude and relaxation both are nouns.

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

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

quietude: a state of peace and quiet
relaxation: a feeling of refreshing tranquility and an absence of tension or worry

Other hyponyms of quietude include ataraxis, heartsease, peace, peace of mind, peacefulness, repose, serenity, easiness.

quietude (noun)	relaxation (noun)
a state of peace and quiet	freedom from activity (work or strain or responsibility)
	the act of making less strict
	a method of solving simultaneous equations by guessing a solution and then reducing the errors that result by successive approximations until all the errors are less than some specified amount
	an occurrence of control or strength weakening
	a feeling of refreshing tranquility and an absence of tension or worry
	(physics) the exponential return of a system to equilibrium after a disturbance
	(physiology) the gradual lengthening of inactive muscle or muscle fibers