turn down vs lower

turn down is not a noun while lower is a noun.

Word	Noun	Adjective	Verb	Adverb
turn down	No	No	Yes	No
lower	Yes	Yes	Yes	No

As verbs, turn down and lower are synonyms defined as:

Other synonyms of turn down include lour.

turn down (noun)	lower (noun)
	the lower of two berths

turn down (adjective)	lower (adjective)
	the bottom one of two

turn down (verb)	lower (verb)
make lower or quieter	make lower or quieter
take a downward direction	set lower
reject with contempt	cause to drop or sink
not accept as true	move something or somebody to a lower position
refuse entrance or membership	look angry or sullen, wrinkle one's forehead, as if to signal disapproval