focal

Etymology

The OED takes it partly as borrowed from Medieval Latin focālis, which in medieval British sources meant having a hearth (1300) or, of wood, used for fuel, and by 1696 also of or relating to a focus, and partly as formed from English focus + -al.^[2] Etymonline and the Oxford Dictionary of English derive it from the New Latin adjective,^[3][4] while Klein, Barnhart and Merriam-Webster treat it as formed in English from focus.^[5][6][7] The Latin adjective is formed from focus (“hearth, fireplace”) with the suffix -ālis;^[2] the Latin noun is of unknown origin.^[3][2] Barnhart compares an Armenian word for flame and traces the noun to Proto-Indo-European *bhok- (“to flame”).^[6] French focal is recorded once in the 15th century for "of a hearth", and since 1812 for "of a focus".^[2]

Earliest recorded meaning

Of a fire: burning in a hearth, in 1639, in T. Phillips's Book of Lamentations; this sense was obsolete after 1848.^[2]

Semantic evolution

The modern senses depend on the noun focus: the German astronomer Johannes Kepler first used Latin focus for a point of convergence in 1604, in a work on optics, and the word entered English in this sense in the 17th century.^[8][6][3] Focal followed in geometry, of a figure described in relation to a focus (1676, in a letter of Edmund Halley), and in optics, of the focus of a lens or mirror (1682, in Flamsteed).^[2] Barnhart and Merriam-Webster date the first use to 1693, in Halley's writings.^[6][7] Johnson (1755) defined it simply as "belonging to the focus".^[9] A figurative sense, marked by the meeting of many elements, and now usually of central importance, is recorded from 1755, in Edward Young.^[2] In the 19th century the word was applied to the centre of a natural process such as an earthquake or volcanic activity (1825) and, in medicine, to disease confined to a focus, localized (1854).^[2][10] Partridge links the scientific senses to the Latin hearth, the seat of the household gods.^[11]

Timeline

• 1639 – of a fire burning in a hearth (obsolete by 1848).^[2]
• 1676 – geometry, relating to or having a focus.^[2]
• 1682 – optics, relating to the focus of a lens or mirror.^[2]
• 1693 – first use according to Barnhart and Merriam-Webster.^[6][7]
• 1755 – figurative, of central importance.^[2]
• 1825 – at the centre of a natural phenomenon such as an earthquake.^[2]
• 1854 – medicine, localized.^[2][10]

Meanings

Adjective

1. Of, relating to, or having a focus, as in optics or geometry.^[12][7][13]
2. Placed at, passing through, or measured from a focus: the focal length of a camera lens.^[12][13][10]
3. Of central importance; being the centre of attention or activity: The square became the focal point of the protests.^[2][10]
4. (medicine) Of a disease or an abnormal process: arising at a particular focus; localized.^[2][10]
5. Relating to the centre or point of origin of a natural process such as an earthquake.^[2]

Word family

• focally
• afocal
• bifocal
• confocal
• focalize
• multifocal

Related words

• focus
• foyer
• fuel

References

1. ^ a b 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 Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
5. ^ Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
6. ^ a b c d e Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
7. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
8. ^ Ayto, John (2005), Word Origins: The Secret Histories of English Words from A to Z, 2nd ed., London: A & C Black
9. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
10. ^ a b c d e Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
11. ^ Partridge, Eric (1966), Origins: A Short Etymological Dictionary of Modern English, 4th ed., London: Routledge & Kegan Paul
12. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins
13. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt