lactose

Etymology

It is borrowed from French lactose,^[2][3][4] which Etymonline and the OED trace to the French chemist Jean-Baptiste Dumas, in his “Traité de chimie appliquée aux arts” (1843);^[2][3] Klein credits the coinage to the French chemist Marcelin Berthelot instead.^[5] It is formed from Latin lac (“milk”), genitive lactis, and the suffix -ose, used for sugars.^[2][3][5] The Latin noun goes back to Proto-Indo-European *g(a)lag- (“milk”).^[3] Barnhart treats the word as formed in English from the Latin genitive and the suffix -ose,^[6][7] and Merriam-Webster as an international scientific word, probably first formed in French.^[4]

Earliest recorded meaning

The sugar present in milk: 1847, in the Medical Times.^[2] Merriam-Webster dates the word to 1857,^[4] Barnhart to 1858,^[6] and Dictionary.com to 1855–60.^[8]

Timeline

• 1843 – lactose in French, in Dumas's treatise on applied chemistry.^[2][3]
• 1847 – milk sugar.^[2] Barnhart dates the English word to 1858.^[6]

Meanings

Noun

1. A slightly sweet disaccharide sugar found in milk, made up of a glucose unit and a galactose unit; also called milk sugar.^{[4][9][10][2]}
2. This sugar as a white crystalline substance used in food processing and in making pharmaceuticals and baby foods.^[10][2][9]

Related words

• lactase
• lactic
• lacteal
• lactation

References

1. ^ a b 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. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ a b 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. ^ Barnhart, Robert K., ed. (1995), The Barnhart Concise Dictionary of Etymology, New York: HarperCollins
8. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
9. ^ a b Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
10. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins