calm down vs still

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

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

As verbs, still is a hypernym of calm down; that is, still is a word with a broader meaning than calm down:

Other hypernyms of calm down include hush, hush up, quieten, shut up, silence.

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

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

calm down (noun)	still (noun)
	an apparatus used for the distillation of liquids; consists of a vessel in which a substance is vaporized by heat and a condenser where the vapor is condensed
	a static photograph (especially one taken from a movie and used for advertising purposes)
	a plant and works where alcoholic drinks are made by distillation
	(poetic) tranquil silence

calm down (adjective)	still (adjective)
	not sparkling
	used of pictures; of a single or static photograph not presented so as to create the illusion of motion; or representing objects not capable of motion
	(of a body of water) free from disturbance by heavy waves
	marked by absence of sound
	not in physical motion
	free from noticeable current

calm down (verb)	still (verb)
become quiet or less intensive	cause to be quiet or not talk
make calm or still	make motionless
become quiet or calm, especially after a state of agitation	make calm or still
	lessen the intensity of or calm

calm down (adverb)	still (adverb)
	to a greater degree or extent; used with comparisons
	with reference to action or condition; without change, interruption, or cessation
	without moving or making a sound
	despite anything to the contrary (usually preceding a concession)