DAILY UPDATED VOCABULARY WITH PICTURES. TREADMILL.

• tread‧mill
• 1 [countable] a piece of exercise equipment that has a large belt around a set of wheels, that you can walk or run on while staying in the same place
• 2 [singular] work or a way of life that seems very boring because you always have to do the same things:
• the treadmill of working in the office
• 3 [countable] a mill worked in the past by prisoners treading on steps fixed to a very large wheel

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.