What does clepsydra mean?
A clepsydra is an ancient timekeeping device, better known simply as a water clock, that measures the passage of time by the controlled flow of water into or out of a container. Marks on the vessel's interior allowed users to read off elapsed hours as the water level rose or fell. Clepsydras were widely used across the ancient Mediterranean and Near East — Egyptian, Greek, Roman, and Chinese civilizations all built them — serving purposes ranging from timing speeches in the Athenian assembly to regulating courtrooms and astronomical observation. The word comes from the Greek for 'water thief', a vivid nod to the way the escaping water seemed to steal time itself. Today 'clepsydra' survives mainly in historical, archaeological, and museum contexts, lending any discussion of early horology a precise, scholarly air. It remains one of the most evocative terms for humanity's earliest attempts to make time visible and measurable.
nounAn ancient device that measures time by the regulated flow of water, typically into or out of a vessel; a water clock.
- A water clock: an ancient time-measuring device in which water flowing at a steady rate into or out of a calibrated vessel marks the passage of time.
"The Athenians used a clepsydra in the courtroom to limit each speaker's allotted speaking time."
"Speakers in Athenian courts watched the clepsydra drain, knowing their argument had to end when the last drop fell."
"Museum curators displayed a reconstructed Roman clepsydra, its bronze float still able to indicate the hour."
'Clepsydras' is the standard English plural; the Latinate 'clepsydrae' occasionally appears in scholarly writing.
"Several surviving clepsydras reveal how precisely ancient engineers could control the flow of water."
The Greeks literally called their water clock a 'water thief' — because it stole time, drop by drop.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of clepsydra
Clepsydra derives directly from the ancient Greek κλεψύδρα (klepsudra), formed from kleptein ('to steal') plus hydōr ('water') — literally a 'water thief'. The term entered English in the early modern period, by the seventeenth century, through Latin scholarly writing on classical antiquity. It shares its first element with words such as kleptomania and kleptocracy, and its second with the many English words of Greek origin built on hydōr, including hydrogen and dehydrate.
How clepsydra is actually used
A learned, somewhat formal word belonging chiefly to historical, archaeological, and scientific writing about ancient technology; in everyday contexts 'water clock' is more common. The plural 'clepsydrae' appears occasionally in scholarly prose, but 'clepsydras' is standard.
Easily confused with clepsydra
An hourglass measures time by the flow of sand, whereas a clepsydra measures it by the flow of water.