treadmill vs exercise device

treadmill and exercise device both are nouns.

Word	Noun	Adjective	Verb	Adverb
treadmill	Yes	No	No	No
exercise device	Yes	No	No	No

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

treadmill: an exercise device consisting of an endless belt on which a person can walk or jog without changing place
exercise device: a device designed to provide exercise for the user

treadmill (noun)	exercise device (noun)
a job involving drudgery and confinement	a device designed to provide exercise for the user
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