Etymologically
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unthinkable

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Pronunciation

  • /ʌnˈθɪŋkəbəl/[1]

Etymology

It is formed from English un- + think + -able.[2][3][4][5] Its Middle English forms include unthenkable and unthencable.[6] The positive thinkable is recorded only from 1764 in the OED, and Etymonline suggests that it may be a back-formation from unthinkable.[2][4]

Earliest recorded meaning

Too great or too many to be conceived; unimaginable: about 1430, in a life of Saint Katherine.[2] Etymonline dates it to the early 15th century.[4]

Semantic evolution

By about 1445 Reginald Pecock used it of what cannot be framed or grasped by thought at all.[2][6] The noun the unthinkable, what cannot be conceived, is recorded from 1871, in Jowett's Plato,[2] and the phrase to think the unthinkable was a philosopher's expression in 1882 before it was weakened, in 1962 in a title by H. Kahn, to considering an unwelcome or unconventional possibility.[2] In colloquial use the adjective also means highly unlikely, or not to be considered at all.[3][7]

Timeline

  • c. 1430 – too great to be conceived; unimaginable.[2]
  • c. 1445 – incapable of being grasped by thought, in Pecock.[2][6]
  • 1871 – noun, the unthinkable.[2]
  • 1882 – to think the unthinkable, in philosophy.[2]
  • 1962 – think the unthinkable, to consider a disturbing possibility.[2]

Meanings

Adjective

  1. Not to be considered; out of the question: Selling the farm was unthinkable to her.[7][5][3]
  2. Impossible to imagine or grasp; inconceivable.[7][5][2]
  3. Contrary to what is reasonable or likely; incredible.[7][5]
  4. Extraordinary; too great to be imagined: unthinkable wealth.[5][2]

Noun

  1. the unthinkable: something that cannot be imagined, or that is out of the question, as in think the unthinkable.[2][5]

Word family

  • unthinkability
  • unthinkably
  • think
  • thinkable

References

  1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c d e f g h i j k l m n Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
  3. ^ a b c Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
  4. ^ a b c Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  5. ^ a b c d e f Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  6. ^ a b c Kurath, Hans; Kuhn, Sherman M.; Lewis, Robert E., eds. (1952–2001), Middle English Dictionary, Ann Arbor: University of Michigan Press; online edition ed. Frances McSparran et al. (2000–2018)
  7. ^ a b c d Collins English Dictionary (2023), Glasgow: HarperCollins