trajectory

Etymology

It is borrowed from New Latin trājectōria,^[2][3][4][5] the feminine of trājectōrius (“of or for throwing across”), a word the OED calls medieval or modern Latin; the OED notes that Newton used the feminine as a noun.^[6][3] The adjective comes from Latin trāiectus (“thrown over or across”), the past participle of trāiciō (“to throw across”),^[3][7][2][8] formed from trāns- (“across”) and iaciō (“to throw”),^[3][7][5] which Etymonline traces to Proto-Indo-European *ye- (“to throw, impel”).^[7] Etymonline gives the Modern Latin form as trājectōrium.^[7] Skeat thought the English word was suggested by Middle French trajectoire, recorded by Cotgrave in 1611.^[9][6] An isolated Middle English traiectorie, a funnel, in a translation of Guy de Chauliac before 1425, came from the same French word, there meaning the end of a funnel, and directly from Medieval Latin trājectōrium (“a funnel”).^[3][7]

Earliest recorded meaning

As an adjective, relating to something thrown or hurled through the air or space: 1668, in the Philosophical Transactions of the Royal Society.^[6][10] As a noun, the path of a body moving under given forces: 1696, in William Whiston's New Theory of the Earth.^[6][3][4] Dictionary.com dates the word to 1660–70^[11] and Etymonline the noun to the 1690s.^[7]

Semantic evolution

The noun began as a term of physics, for the path of any body moving under given forces;^[6][7] Weekley notes that artillerists gave it the special sense of the path of a projectile.^[12] Mathematicians used it from 1795 for a curve or surface that cuts a family of curves at a given angle.^[6][13] The figurative sense, a path or line of development, is recorded from 1838,^[6][7] and is now common, as in a career's trajectory.^[4] The adjective was also used in physiology from 1747 for a gland into which lymphatic vessels carry their fluid, a sense the OED marks as probably obsolete.^[6]

Timeline

• before 1425 – isolated Middle English traiectorie, a funnel.^[3]
• 1668 – adjective, relating to something thrown through the air or space.^[6]
• 1696 – noun, the path of a body moving under given forces.^[6][3][4]
• 1747 – adjective, in physiology, of a gland that receives lymphatic vessels.^[6]
• 1795 – in geometry, a curve cutting a series of curves according to a given law.^[6]
• 1838 – figurative and transferred use.^[6][7]
• 1861 – rarely, a projectile such as a bullet.^[6]

Meanings

Noun

1. The path that a moving body follows through the air or space under forces such as thrust and gravity, especially the curved path of a projectile or the orbit of a planet or comet: The ball's trajectory carried it over the fence.^[13][4][6]
2. A course of progress or development compared to such a path: the upward trajectory of her career.^[4][6]
3. In geometry, a curve that cuts every curve or surface of a given family at a constant angle.^[13][6]

Adjective

1. Relating to a trajectory, or to something thrown through the air or space.^[4][6]

Related words

• traject
• project
• jet

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
3. ^ a b c d e f g h Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
4. ^ a b c d e f g Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ a b Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
6. ^ a b c d e f g h i j k l m n o p q r Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
7. ^ a b c d e f g h i Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
8. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
9. ^ Skeat, Walter W. (1911), A Concise Etymological Dictionary of the English Language, new ed., Oxford: Clarendon Press
10. ^ Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
11. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
12. ^ Weekley, Ernest (1921), An Etymological Dictionary of Modern English, London: John Murray
13. ^ a b c Collins English Dictionary (2023), Glasgow: HarperCollins