rest period vs intermission

rest period and intermission both are nouns.

Word	Noun	Adjective	Verb	Adverb
rest period	Yes	No	No	No
intermission	Yes	No	No	No

As nouns, intermission is a hypernym of rest period; that is, intermission is a word with a broader meaning than rest period:

rest period: a pause for relaxation
intermission: a time interval during which there is a temporary cessation of something

Other hypernyms of rest period include break, interruption, pause, suspension.

rest period (noun)	intermission (noun)
a pause for relaxation	the act of suspending activity temporarily
	a time interval during which there is a temporary cessation of something