gristmill vs milling machinery

gristmill and milling machinery both are nouns.

Word	Noun	Adjective	Verb	Adverb
gristmill	Yes	No	No	No
milling machinery	Yes	No	No	No

As nouns, milling machinery is a hypernym of gristmill; that is, milling machinery is a word with a broader meaning than gristmill:

gristmill: a mill for grinding grain (especially the customer's own grain)
milling machinery: machinery that processes materials by grinding or crushing

Other hypernyms of gristmill include grinder, mill.

gristmill (noun)	milling machinery (noun)
a mill for grinding grain (especially the customer's own grain)	machinery that processes materials by grinding or crushing