Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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