What does clepsydrae mean?
A clepsydra is an ancient instrument for measuring time by means of water — typically a vessel that either fills with or drains water at a steady rate, with markings indicating the passing hours. 'Clepsydrae' is its plural form, referring to two or more such devices. Water clocks were among the earliest timekeeping technologies known, used in ancient Egypt, Babylon, Greece, Rome, China, and elsewhere, especially where sundials failed — indoors or under cloudy skies. The term appears almost exclusively in scholarly writing about classical antiquity, archaeology, and the history of horology; in general usage, the plain English phrase 'water clock' is preferred. The word derives from the Greek klepsydra, combining words meaning 'to steal' and 'water' — literally a 'water thief.' Knowing 'clepsydrae' signals familiarity with classical vocabulary and the long pre-mechanical history of measuring time.
nounClepsydrae is the plural of clepsydra: an ancient device that measured time by the regulated flow of water into or out of a vessel.
- The plural form of 'clepsydra': an ancient instrument for measuring time by the flow of water.
"The museum's collection of ancient timepieces included several Egyptian and Roman clepsydrae."
"Archaeologists uncovered fragments of Athenian clepsydrae used to time speeches in the law courts."
"The exhibit traced the history of timekeeping from simple outflow clepsydrae to elaborate astronomical water clocks."
As a noun borrowed from Greek via Latin, clepsydra takes the classical plural clepsydrae, though the anglicized clepsydras is also widely used.
"Several well-preserved clepsydrae were recovered from the site."
Long before mechanical clocks existed, people told time by watching water slowly drain through a hole — and courts in ancient Athens used these water clocks to limit how long speakers could talk.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of clepsydrae
Clepsydrae is the Latinized plural of clepsydra, which comes from the Greek klepsydra, formed from kleptein ('to steal') and hydōr ('water') — literally a 'water thief,' describing how the device's outflow siphons off measured amounts of water. The same roots gave English other words: kleptomania from kleptein, and hydraulic, hydrology, and hydrant from hydōr. The term entered European scholarly language via Latin texts on ancient instruments and remains standard in academic treatments of ancient timekeeping.
Related word forms
How clepsydrae is actually used
The word belongs to formal, academic registers — history of science, archaeology, and classical studies — and is rare in everyday speech. In ordinary contexts, 'water clock' is far more common. The anglicized plural 'clepsydras' also occurs alongside the classical 'clepsydrae'.
Easily confused with clepsydrae
A clepsydra is a single water-clock device, while clepsydrae is simply its plural form referring to more than one such device.