turn down vs refuse

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

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

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

Other hypernyms of turn down include decline.

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

Other synonyms of turn down include decline, pass up, reject.

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

Other synonyms of turn down include reject, turn away.

turn down (noun)	refuse (noun)
	food that is discarded (as from a kitchen)

turn down (verb)	refuse (verb)
make lower or quieter	show unwillingness towards
take a downward direction	not accept as true
reject with contempt	refuse to let have
not accept as true	refuse entrance or membership
refuse entrance or membership	elude, especially in a baffling way
	resist immunologically the introduction of some foreign tissue or organ