settle down vs simmer down

settle down and simmer down both are verbs.

Word	Noun	Adjective	Verb	Adverb
settle down	No	No	Yes	No
simmer down	No	No	Yes	No

As verbs, settle down and simmer down are synonyms defined as:

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

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

settle down (verb)	simmer down (verb)
become settled or established and stable in one's residence or life style	become quiet or calm, especially after a state of agitation
become quiet or calm, especially after a state of agitation
settle into a position, usually on a surface or ground