/ˈsɪŋkrənəs/
[adjective] Happening at the same time or at the same speed as something else. In technology, it describes systems or processes that operate in a coordinated way, staying in step with each other.
This word was born from the ancient Greek obsession with measuring the cosmos — it originally described stars moving in perfect celestial lockstep.
To understand 'synchronous', you need to pull it apart at its seams. It comes from the Greek word 'synchronos', which is itself built from two smaller pieces: 'syn', meaning 'together' or 'with', and 'chronos', meaning 'time'. Chronos was not just a concept for the ancient Greeks — it was a god, a vast and ancient deity who personified time itself, often depicted as an old man with a long beard, holding the tools of fate. When Greek thinkers wanted to say that two things happened at exactly the same moment, they reached for this powerful pairing.
The word entered scientific Latin as 'synchronus' during the Renaissance, when European scholars were conducting a furious, exhilarating rediscovery of Greek scientific texts. Astronomers in particular needed precise language to describe celestial events — eclipses, planetary conjunctions, the way the moon seemed to keep perfect pace with the Earth's rotation. 'Synchronus' was exactly the word they needed, and it began appearing in Latin astronomical and philosophical writing during the 16th century.
English adopted 'synchronous' in the 17th century, with early recorded uses appearing around the 1660s. At first, it lived almost entirely in scientific and scholarly writing. Writers used it to describe events in natural history or physics that occurred simultaneously — two chemical reactions, the beating of two hearts, the oscillation of pendulums. The great Dutch physicist Christiaan Huygens famously noticed in 1665 that two pendulum clocks hung on the same wall would eventually swing in perfect unison, a phenomenon that cried out for exactly this word.
The Greek root 'chronos' has been extraordinarily productive in English, threading itself through dozens of familiar words. 'Chronos' → Latin 'chronus' → English gave us 'chronic' (lasting a long time), 'chronicle' (a record ordered by time), 'chronology' (the arrangement of events in time), and 'anachronism' (something placed in the wrong time). The prefix 'syn' similarly travelled from Greek into scientific English and produced words like 'synthesis' (putting things together), 'synonym' (words with the same meaning), and 'synergy' (forces working together). In 'synchronous', both of these richly travelled roots meet.
In the 20th century, 'synchronous' leapt from the pages of scientific journals into everyday life, driven largely by the rise of technology and telecommunications. Engineers designing electrical grids needed motors that turned at exactly the rate dictated by the alternating current — these became known as 'synchronous motors'. The space age brought 'synchronous orbit', describing satellites that move at precisely the speed of Earth's rotation and therefore appear to hang motionless in the sky. Then came computing and the internet, where 'synchronous' took on a fresh, practical meaning: a communication is synchronous if both people participate at the same time, like a phone call, as opposed to 'asynchronous' communication like email, where responses can arrive at any moment.
What is quietly remarkable about this word is how it connects ancient mythological time — the devouring, unstoppable god Chronos — to the most modern, mundane questions of digital life, like whether a work meeting happens live or recorded. A word forged to describe the movements of stars now governs how we organise our video calls. Time, it turns out, has always been the thing we most urgently need to coordinate.