The Collaborative International Dictionary of English v.0.48:

Clockwork \Clock"work`\ (-w[^u]rk`), n.
   The machinery of a clock, or machinery resembling that of a
   clock; machinery which produces regularity of movement.
   [1913 Webster]

WordNet (r) 3.0 (2006):

clockwork
    n 1: any mechanism of geared wheels that is driven by a coiled
         spring; resembles the works of a mechanical clock