asynchronous

Etymology

It is formed from English a- + synchronous, with the Greek prefix meaning "not, without".^{[2][3][4][5][6]} Synchronous is from Late Latin synchronus (“simultaneous”),^[2][3][7] from Ancient Greek σύγχρονος (súnkhronos, “happening at the same time”),^[2][3] formed from σύν (sún, “together, with”) and χρόνος (khrónos, “time”).^[2][3][7] The related noun asynchronism is recorded from 1850.^[3]

Earliest recorded meaning

Not occurring at the same time, not coinciding in time: 1737, in a translation of F. Nicholls in the Medical Essays and Observations.^[2] Etymonline dates the adjective to 1735,^[3] Merriam-Webster Unabridged gives 1748 as its first known use,^[4] and Dictionary.com dates it to 1740–50.^[6]

Semantic evolution

For more than a century the word kept its general sense of things that do not happen together.^[2][5] From 1893 electrical engineers used it of an alternating-current motor or generator that can run at speeds other than the one fixed by the frequency of the current.^[2] With the computer it gained two technical senses: from 1953, of a machine or operation not timed by clock signals, each step starting when the previous one ends; since 1966 it has also described data transmission in which packets are sent at irregular intervals, each marked at its start and end by special signals.^[2] The OED compares the parallel computing sense of synchronous.^[2] Since 1976 it has also described a satellite orbit in which the satellite circles its planet at a rate different from the planet's own rotation.^[2]

Timeline

• 1737 – not occurring at the same time.^[2]
• 1893 – of an alternating-current motor or generator, not running at the speed fixed by the frequency.^[2]
• 1953 – of a computer or its operations, not timed by clock signals.^[2]
• 1966 – of data transmission, sent at irregular intervals with start and stop signals.^[2]
• 1976 – of an orbit or satellite, not matching the rotation of the parent body.^[2]

Meanings

Adjective

1. Not happening or existing at the same time; not simultaneous: asynchronous movements of the two pistons.^[4][2]
2. Of digital communication or data transmission: sent without a fixed timing, the start and end of each character or packet being marked by its own signals.^[4][2]
3. (computing) Of a computer or an operation: not governed by a clock signal, each step beginning when the one before it is finished.^[2]
4. (electrical engineering) Of an alternating-current motor or generator: able to run at speeds other than the one set by the frequency of the current.^[2]

Word family

• asynchronously

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n o p q r s Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ a b Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
6. ^ a b Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
7. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt