onus

Etymology

It is borrowed from Latin onus (“load, burden”),^{[2][3][4][5][6]} genitive oneris,^[4][7] which in Latin was also used figuratively for a tax or expense and for trouble or difficulty.^[3] De Vaan reconstructs the Latin noun as a Proto-Indo-European neuter s-stem meaning "load",^[8] and Etymonline gives the root as Proto-Indo-European *en-es- (“burden”).^[3] The OED, Barnhart, Klein and de Vaan relate it to a Sanskrit word for a cart or wagon,^[2][4][7][8] and Barnhart and Partridge compare, more doubtfully, Ancient Greek ἀνία (anía, “grief, distress”), Aeolic ὀνία (onía).^[4][9][8] The Latin noun is also the source of onerōsus, whence onerous, and of exonerō (“to unload”), whence exonerate.^[9][4][8]

Earliest recorded meaning

A burden, a responsibility or duty: 1626, in a sermon by Bishop Henry King, in the OED's revised entry.^[2] Merriam-Webster Unabridged also dates the word to 1626,^[10] while Etymonline and Barnhart give the 1640s or about 1640, and Dictionary.com 1630–40.^[3][4][11]

Semantic evolution

The word kept the figurative Latin sense of a burden laid on someone, and it is often used with the, as in the onus is on them.^[2][12] The legal phrase onus probandi, the burden of proving what one alleges, came into English in 1722, according to Etymonline,^[3] and the OED takes the legal sense of onus alone, as in onus of proof, from it, with a first record in 1827.^[2][13] Merriam-Webster Unabridged also records a sense of something distasteful that is hard to bear.^[10]

Timeline

• 1626 – a burden, responsibility or duty.^[2][10]
• 1722 – onus probandi, the burden of proof, in legal Latin.^[3]
• 1827 – onus of proof, the obligation to prove what one asserts.^[2]

Meanings

Noun

1. A responsibility, duty or burden, especially a hard or unwelcome one: The onus is on the landlord to repair the roof.^[12][10][2]
2. (law) The obligation to prove what one asserts; the burden of proof, also called onus of proof or onus probandi.^[2][13]
3. Something distasteful or objectionable that is difficult to bear.^[10]

Related words

• onerous
• exonerate

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e f Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
5. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
6. ^ Weekley, Ernest (1921), An Etymological Dictionary of Modern English, London: John Murray
7. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
8. ^ a b c d de Vaan, Michiel (2008), Etymological Dictionary of Latin and the other Italic Languages, Leiden Indo-European Etymological Dictionary Series 7, Leiden; Boston: Brill
9. ^ a b Partridge, Eric (1966), Origins: A Short Etymological Dictionary of Modern English, 4th ed., London: Routledge & Kegan Paul
10. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
11. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
12. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins
13. ^ a b Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press