candela

Etymology

It is borrowed from Latin candēla (“candle”),^[2][3][4] modelled on the earlier use of candle as a unit of illuminating power.^[2] The Latin word comes from candeō (“to shine, glow”),^[5][3][6] from Proto-Indo-European *kand- (“to shine”).^[3][6] That older word is a much earlier borrowing of the same Latin noun,^[6][1] and chandelle is a third form of it.^[1]

Earliest recorded meaning

The unit of luminous intensity: 1948, in the journal Light and Lighting.^[2] Merriam-Webster's first date is 1949,^[7] and Etymonline's is 1950.^[3]

Semantic evolution

The English word candle had served as a unit of illuminating power since 1866, based on a standard spermaceti candle and often called the international candle.^[2] Candela keeps the Latin form for the same purpose, and Collins and Merriam-Webster still equate it with candle in this sense.^[8][7] Its definition has changed: an older one, kept in the Shorter Oxford, is based on the light from a black body at the solidifying point of platinum,^[9] and the current one on radiation of a fixed frequency.^[8][2]

Timeline

• 1866 – candle as a unit of illuminating power.^[2]
• 1948 – candela, a unit of luminous intensity.^[2] Merriam-Webster dates it to 1949 and Etymonline to 1950.^[7][3]

Meanings

Noun

1. The basic SI unit of luminous intensity, symbol cd, defined by a source that emits light of a frequency of 540 × 10¹² hertz with a radiant intensity of 1/683 watt per steradian in a given direction.^[8][2]

Related words

• candelabrum
• candid
• candidate
• candle
• candlepower
• candlestick
• chandler
• chandlery

References

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