coffee mill vs coffee grinder

coffee mill and coffee grinder both are nouns.

Word	Noun	Adjective	Verb	Adverb
coffee mill	Yes	No	No	No
coffee grinder	Yes	No	No	No

As nouns, coffee mill and coffee grinder are synonyms defined as:

coffee mill (noun)	coffee grinder (noun)
a mill that grinds roasted coffee beans	a mill that grinds roasted coffee beans