chill out vs simmer down

chill out and simmer down both are verbs.

Word	Noun	Adjective	Verb	Adverb
chill out	No	No	Yes	No
simmer down	No	No	Yes	No

As verbs, chill out and simmer down are synonyms defined as:

chill out and simmer down: become quiet or calm, especially after a state of agitation

Other synonyms of chill out include calm, calm down, cool it, cool off, settle down.

chill out (verb)	simmer down (verb)
become quiet or calm, especially after a state of agitation	become quiet or calm, especially after a state of agitation