inertia

Etymology

It is borrowed from New Latin inertia,^[2][3] a specialized use of Latin inertia (“unskilfulness; inactivity, idleness”),^[4][2][5][6] from iners (“unskilled; inactive”),^[4][2][5] the source of inert.^[7][2] Iners is formed from in- (“not”) and ars (“skill, art”).^[7][4] The Latin word was introduced into physics by the German astronomer Johannes Kepler,^[4][2][5][6] and Newton used it in his “Principia” (1687).^[2][5]

Earliest recorded meaning

The property of matter by which it stays at rest or keeps moving uniformly in a straight line unless an outside force acts on it: 1713, in William Derham's Physico-Theology.^[4][2][3]

Semantic evolution

Early English examples treat the word as Latin, or use the Latin phrase vis inertiae, force of inertia, until the early 1700s.^[2][5] In the late 19th century physicists extended it to other quantities that resist change, as in electric inertia (1886) and later thermal inertia,^[4][8][9] and photographers used it for a value from which the speed of an emulsion is calculated.^[4][8] The Latin sense of inactivity and sluggishness came back in English in 1821, in De Quincey's Confessions of an English Opium-Eater;^[4][2][5] the Oxford Dictionary of English counts this as the earliest sense of the word.^[10]

Timeline

• 1713 – physics, the tendency of matter to keep its state of rest or motion.^[4][2][3]
• 1821 – inactivity, disinclination to act; sloth, apathy.^[4][2] Etymonline dates it to 1822.^[5]
• 1886 – electric inertia, a circuit's resistance to sudden changes of current.^[4]
• c. 1886 – photography, the exposure value used to calculate the speed of an emulsion.^[4]

Meanings

Noun

1. In physics, the property of a body by which it stays at rest or keeps moving uniformly in a straight line unless an external force acts on it.^[3][9][4]
2. A similar resistance to change in other physical quantities: thermal inertia.^[9][3][8]
3. Unwillingness to act or change; inactivity, sluggishness or apathy: Bureaucratic inertia delayed the reforms for years.^[9][3][4]
4. In photography, the exposure from which the speed of an emulsion is calculated.^[4][8]

Word family

• inertial
• inertially
• moment of inertia

Related words

• inert
• art

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
3. ^ a b c d e f Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
4. ^ a b c d e f g h i j k l m n o Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
5. ^ a b c d e f g Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
6. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
7. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
8. ^ a b c d Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
9. ^ a b c d Collins English Dictionary (2023), Glasgow: HarperCollins
10. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press