mill vs pepper grinder

mill and pepper grinder both are nouns.

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

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

mill (noun)	pepper grinder (noun)
the act of grinding to a powder or dust	a mill for grinding pepper
machinery that processes materials by grinding or crushing
a plant consisting of one or more buildings with facilities for manufacturing

mill (verb)	pepper grinder (verb)
grind with a mill
produce a ridge around the edge of
roll out (metal) with a rolling machine
move about in a confused manner