milk sugar vs lactose

milk sugar and lactose both are nouns.

Word	Noun	Adjective	Verb	Adverb
milk sugar	Yes	No	No	No
lactose	Yes	No	No	No

As nouns, milk sugar and lactose are synonyms defined as:

milk sugar and lactose: a sugar comprising one glucose molecule linked to a galactose molecule; occurs only in milk

milk sugar (noun)	lactose (noun)
a sugar comprising one glucose molecule linked to a galactose molecule; occurs only in milk	a sugar comprising one glucose molecule linked to a galactose molecule; occurs only in milk