milk shake vs milkshake

milk shake and milkshake both are nouns.

Word	Noun	Adjective	Verb	Adverb
milk shake	Yes	No	No	No
milkshake	Yes	No	No	No

As nouns, milk shake and milkshake are synonyms defined as:

milk shake and milkshake: frothy drink of milk and flavoring and sometimes fruit or ice cream

Other synonyms of milk shake include shake.

milk shake (noun)	milkshake (noun)
frothy drink of milk and flavoring and sometimes fruit or ice cream	frothy drink of milk and flavoring and sometimes fruit or ice cream