shrink vs scale down

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

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

As verbs, scale down is a hyponym of shrink; that is, scale down is a word with a more specific, narrower meaning than shrink:

Other hyponyms of shrink include reduce, reef, miniaturise, miniaturize, depopulate, desolate, downsize, contract.

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

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