skim milk vs skimmed milk

skim milk and skimmed milk both are nouns.

Word	Noun	Adjective	Verb	Adverb
skim milk	Yes	No	No	No
skimmed milk	Yes	No	No	No

As nouns, skim milk and skimmed milk are synonyms defined as:

skim milk (noun)	skimmed milk (noun)
milk from which the cream has been skimmed	milk from which the cream has been skimmed