pipe down vs silence

pipe down is not a noun while silence is a noun.

Word	Noun	Adjective	Verb	Adverb
pipe down	No	No	Yes	No
silence	Yes	No	Yes	No

pipe down (noun)	silence (noun)
	the absence of sound
	a refusal to speak when expected
	the trait of keeping things secret
	the state of being silent (as when no one is speaking)

pipe down (verb)	silence (verb)
become quiet or quieter	cause to be quiet or not talk
	keep from expression, for example by threats or pressure