treadmill vs line of work

treadmill and line of work both are nouns.

Word	Noun	Adjective	Verb	Adverb
treadmill	Yes	No	No	No
line of work	Yes	No	No	No

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

Other hypernyms of treadmill include business, job, line, occupation.

treadmill (noun)	line of work (noun)
a job involving drudgery and confinement	the principal activity in your life that you do to earn money
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