scale down vs shrink

scale down is not a noun while shrink is a noun.

Word	Noun	Adjective	Verb	Adverb
scale down	No	No	Yes	No
shrink	Yes	No	Yes	No

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

Other hypernyms of scale down include reduce.

scale down (noun)	shrink (noun)
	a physician who specializes in psychiatry

scale down (verb)	shrink (verb)
reduce proportionally	become smaller or draw together
make smaller	reduce in size; reduce physically
	wither, as with a loss of moisture
	decrease in size, range, or extent
	draw back, as with fear or pain