Etymologically
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diagonal

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Pronunciation

  • /daɪ̯ˈæɡ(ə)nəl/[1]
  • US: /daɪ̯ˈeɪ̯ɡ(ə)nəl/[1]

Etymology

It is borrowed from Latin diagōnālis,[2][3][4][5] a word used by Vitruvius;[2] in Barnhart, Etymonline and Skeat it is borrowed from Middle French diagonal, from the Latin.[6][7][8] The French word is recorded from the 13th century.[2] The Latin adjective is from diagōnus (“slanting line”),[6][7] from Ancient Greek διαγώνιος (diagṓnios, “from angle to angle”),[2][3][9] formed from διά (diá, “across, through”) and γωνία (gōnía, “angle, corner”),[2][7][9] as in polygon.[9] The Greek word for angle is related to γόνυ (gónu, “knee”) and so to English knee and genuine;[6][10][9] Etymonline traces it to Proto-Indo-European *genu- (“knee; angle”).[7]

Earliest recorded meaning

Of a line, running from one angle of a figure to an opposite, not adjacent angle: the OED's first record is from about 1541, in Copland's translation of Guy de Chauliac's surgery;[2] Barnhart dates the adjective to 1563, implied earlier in the adverb diagonally, in 1541 and in a Middle English translation of Chauliac's Grande Chirurgie probably before 1425.[6]

Semantic evolution

Ayto notes that the strict geometric meaning, a line joining two angles of a figure that are not next to each other, shows the origin better than the common loose use for "oblique".[9] The noun, a diagonal line, is recorded from 1571, in a geometry by Digges.[2][7][10] The looser sense of slanting or oblique followed in 1665,[2] and the sense "marked with oblique lines" before 1679.[2] Johnson (1755) defined the adjective as reaching from one angle to another so as to divide a parallelogram into equal parts.[11] The noun was later applied to a row of squares in chess,[7][12] to a beam or plank set slantwise in a structure (1837),[2] and to a cloth woven with diagonal ribs (1861).[2][12]

Timeline

  • before 1425 – implied in the adverb diagonally.[6]
  • c. 1541 – of a line, joining non-adjacent angles of a figure.[2]
  • 1563 – the adjective, in Barnhart's dating.[6][10]
  • 1571 – noun, a diagonal line.[2][10]
  • 1665 – slanting, oblique.[2]
  • before 1679 – marked with oblique lines.[2]
  • 1837 – a beam or plank set diagonally in a structure.[2]
  • 1861 – a cloth woven with diagonal ribs.[2]

Meanings

Adjective

  1. (mathematics) Joining two vertices of a polygon that are not next to each other, or two vertices of a polyhedron not on the same face.[12][10][2]
  2. Running at a slant; oblique: The path cut a diagonal line across the lawn.[12][10][2]
  3. Marked with slanting lines or patterns: a diagonal weave.[12][2]

Noun

  1. (mathematics) A diagonal line or plane.[12][10][2]
  2. (chess) A slanting row of squares of the same colour.[12][7]
  3. A slanting direction, row or pattern.[10]
  4. A cloth woven with slanting ribs, such as twill.[12][2]
  5. A part of a structure, such as a beam, set slantwise.[2]

Word family

  • diagonally
  • diagonalize
  • nondiagonal
  • diagonal matrix
  • main diagonal

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 r s t u v w Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
  3. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
  4. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
  5. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
  6. ^ a b c d e f Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
  7. ^ a b c d e f g Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  8. ^ Skeat, Walter W. (1911), A Concise Etymological Dictionary of the English Language, new ed., Oxford: Clarendon Press
  9. ^ a b c d e Ayto, John (2005), Word Origins: The Secret Histories of English Words from A to Z, 2nd ed., London: A & C Black
  10. ^ a b c d e f g h Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  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 c d e f g h Collins English Dictionary (2023), Glasgow: HarperCollins