relaxation vs inactivity

relaxation and inactivity both are nouns.

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

As nouns, inactivity is a hypernym of relaxation; that is, inactivity is a word with a broader meaning than relaxation:

relaxation (noun)	inactivity (noun)
freedom from activity (work or strain or responsibility)	being inactive; being less active
the act of making less strict	a disposition to remain inactive or inert
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	the state of being inactive
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