名詞 tread-mill:

1. an exercise device consisting of an endless belt on which a person can walk or jog without changing place
   同義詞：treadmill
2. a mill that is powered by men or animals walking on a circular belt or climbing steps
   同義詞：treadmill, treadwheel, tread-wheel
3. a job involving drudgery and confinement
   同義詞：treadmill, salt mine