improbable

Etymology

The OED takes it as borrowed from Latin improbābilis, formed from in- (“not”) and probābilis (“probable, likely”), and compares improbable, first recorded in Cotgrave in 1611.^[2][3] The Shorter Oxford, the Oxford Dictionary of English and Merriam-Webster allow French or Latin as the source.^[4][5][6] Barnhart and Etymonline take it as probably formed from English im- + probable, perhaps after Italian improbabile, or else from Latin.^[7][8] The Latin adjective meant "hard to prove" or "not deserving of approval",^[4][3] and probābilis comes from probō (“to test, prove”), the source of prove.^[3][9]

Earliest recorded meaning

Not likely to be true or to happen: 1598, in Florio's Italian–English dictionary A Worlde of Wordes.^[2][7] Etymonline and Dictionary.com also date the word to the 1590s.^[8][10]

Semantic evolution

The sense has stayed close to "unlikely" since 1598.^[2] By 1617 it qualified a clause, as in "it is improbable that…",^[2] and by 1659 it could also describe a person or thing unlikely to suit, or one that does not look the part.^[2] Johnson (1755) defined it as "unlikely; incredible".^[11] Merriam-Webster and the Shorter Oxford also record it for things that are unlikely yet real or true.^[6][4]

Timeline

• 1598 – not likely to be true or to happen, in Florio.^[2][7]
• 1617 – qualifying a clause, it is improbable that.^[2]
• 1659 – unlikely to suit, or not looking the part.^[2]

Meanings

Adjective

1. Not probable; unlikely to be true or to happen; hard to believe: It seems improbable that the train will arrive on time.^[12][6][2]
2. Unlikely, yet real or true: The underdogs staged an improbable comeback.^[6][4]

Word family

• improbableness
• improbably
• improbability
• superimprobable

Related words

• probability
• probably
• probable
• prove

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 Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
4. ^ a b c d Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
5. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
6. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
7. ^ a b c Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
8. ^ a b Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
9. ^ Partridge, Eric (1966), Origins: A Short Etymological Dictionary of Modern English, 4th ed., London: Routledge & Kegan Paul
10. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
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. ^ Collins English Dictionary (2023), Glasgow: HarperCollins