skimmed milk vs skim milk

skimmed milk and skim milk both are nouns.

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

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

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