'Water clock' definitions:

Definition of 'water clock'

(from WordNet)
noun
Clock that measures time by the escape of water [syn: water clock, clepsydra, water glass]

Definition of 'Water clock'

From: GCIDE
  • Water clock \Wa"ter clock`\ An instrument or machine serving to measure time by the fall, or flow, of a certain quantity of water; a clepsydra. [1913 Webster]