[tread.mill] n (1822) 1 a: a mill worked by persons treading on steps on the periphery of a wide wheel having a horizontal axis and used formerly in prison punishment b: a mill worked by an animal treading an endless belt c: a device having an endless belt on which an individual walks or runs in place for exercise or physiological testing
2: a wearisome or monotonous routine resembling continued activity on a treadmill