treadmill vs milling machinery

treadmill and milling machinery both are nouns.

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

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

treadmill: a mill that is powered by men or animals walking on a circular belt or climbing steps
milling machinery: machinery that processes materials by grinding or crushing

Other hypernyms of treadmill include grinder, mill.

treadmill (noun)	milling machinery (noun)
a job involving drudgery and confinement	machinery that processes materials by grinding or crushing
a mill that is powered by men or animals walking on a circular belt or climbing steps
an exercise device consisting of an endless belt on which a person can walk or jog without changing place