grinder vs coffee mill

grinder and coffee mill both are nouns.

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

As nouns, coffee mill is a hyponym of grinder; that is, coffee mill is a word with a more specific, narrower meaning than grinder:

grinder (noun)	coffee mill (noun)
a machine tool that polishes metal	a mill that grinds roasted coffee beans
machinery that processes materials by grinding or crushing
grinding tooth with a broad crown; located behind the premolars
a large sandwich made of a long crusty roll split lengthwise and filled with meats and cheese (and tomato and onion and lettuce and condiments); different names are used in different sections of the United States