calm down vs calm

calm down is not a noun while calm is a noun.

Word	Noun	Adjective	Verb	Adverb
calm down	No	No	Yes	No
calm	Yes	Yes	Yes	No

As verbs, calm down and calm are synonyms defined as:

Other synonyms of calm down include lull, quiet, quieten, still, tranquilize, tranquillise, tranquillize.

As verbs, calm down and calm are synonyms defined as:

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

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

calm down (noun)	calm (noun)
	steadiness of mind under stress
	wind moving at less than 1 knot; 0 on the Beaufort scale

calm down (adjective)	calm (adjective)
	(of weather) free from storm or wind
	not agitated; without losing self-possession

calm down (verb)	calm (verb)
become quiet or less intensive	cause to be calm or quiet as by administering a sedative to
make calm or still	make steady
become quiet or calm, especially after a state of agitation	make calm or still
	become quiet or calm, especially after a state of agitation