WordNet (r) 3.0 (2006):

squirrel cage
    n 1: cage with a cylindrical framework that rotates as a small
         animal runs inside it

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "squirrel cage":
   beat, beaten path, broken record, bureaucracy, bureaucratism,
   chinoiserie, daily grind, grind, groove, humdrum, invariability,
   irk, irksomeness, jog trot, monotony, red tape, red-tapeism, round,
   routine, run, rut, sameliness, sameness, tedium, the beaten track,
   the daily round, the round, the squirrel cage, the treadmill,
   the weary round, track, treadmill, undeviation, unvariation,
   wearisome sameness, well-worn groove