parallax

Etymology

It is borrowed from Middle French parallaxe,^{[2][3][4][5][6]} and the OED and the Shorter Oxford also give New Latin parallaxis as a source.^[5][6] Both are from Ancient Greek παράλλαξις (parállaxis, “change, alternation”),^[5][3][2][7] which in Hellenistic Greek was already a term of astronomy.^[5] The Greek noun is from παραλλάσσω (parallássō, “to alter, make alternate”),^[5][3][2] formed from παρα- (para-, “beside”) and ἀλλάσσω (allássō, “to change, exchange”),^[5][3][2] from ἄλλος (állos, “other”).^[8][2][7][3] The French word is recorded in astronomy from 1557, and the Latin one from 1574.^[5] The OED takes the rare sense "a change" directly from Greek.^[5]

Earliest recorded meaning

The difference in the apparent position of an object seen from two different points: about 1574, in W. Bourne's Regiment for Sea.^[5][4] Etymonline dates the word to the 1570s, Barnhart's concise dictionary to 1580 and the full edition to 1594.^[2][9][3]

Semantic evolution

In Greek the noun meant change or alternation, and also the inclination of two lines meeting at an angle, before astronomers used it for an apparent shift in position.^[3][2][5] English took it in that astronomical and navigational sense,^[5][2] and almost at once used it figuratively for distortion, the fact of seeing wrongly, recorded from 1595.^[5][6][10] Johnson (1755) defined it as the distance between the true and apparent place of the sun or a star seen from the earth's surface, and quoted Milton's "By what strange parallax or optick skill" from Paradise Regained.^[11] In 1677 the word was used once for a change in general, a sense now obsolete.^[5] Photography added a further sense in the 20th century: a defect in a photograph caused by differences in the positions of parts of the camera, recorded from 1935.^[5]

Timeline

• c. 1574 – the difference in the apparent position of an object seen from two points, especially in astronomy.^[5][4]
• 1595 – figurative, distortion; seeing wrongly.^[5][6]
• 1677 – a change, an alteration (obsolete, rare).^[5]
• 1935 – in photography, a fault in an image caused by the different positions of parts of the camera.^[5]

Meanings

Noun

1. The apparent shift in the position or direction of an object when it is seen from two different points: Close one eye and then the other, and the parallax makes your thumb seem to jump.^[4][12][5]
2. (astronomy) The angle that measures this shift for a celestial body, used to find its distance, as when a nearby star is observed from opposite points of the earth's orbit.^[12][6][4]
3. (photography) A defect in a photograph caused by differences in the positions of parts of the camera, especially wrong framing of the image.^[5]
4. Distortion; the fact of seeing something wrongly, now usually figurative.^[5][6]

Word family

• parallactic
• parallactically
• parsec

Related words

• parallel
• alien
• else

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
3. ^ a b c d e f g Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
4. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ a b c d e f g h i j k l m n o p q r s t u Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
6. ^ a b c d e f Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
7. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
8. ^ Weekley, Ernest (1921), An Etymological Dictionary of Modern English, London: John Murray
9. ^ Barnhart, Robert K., ed. (1995), The Barnhart Concise Dictionary of Etymology, New York: HarperCollins
10. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
11. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
12. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins