impenetrable

Etymology

It is inherited from Middle English impenetrabel,^[2][3][4] borrowed from Middle French impénétrable,^[5][2][3][6] recorded in French from the 14th century,^[7][8] and directly borrowed from Latin impenetrābilis (“that cannot be penetrated”).^[8][5][9] The Latin adjective is formed from in- (“not”) and penetrābilis (“that can be pierced”),^{[7][10][3][8]} from penetrō (“to penetrate”).^[10]

Earliest recorded meaning

Impossible to get into or through: 1447, in Bokenham's verse lives of saints, which call the Son of God an impenetrable wall.^[9][5] The OED's first quotation, from Capgrave's Chronicle (before 1464), describes a strong helmet.^[7][9]

Semantic evolution

The figurative sense, whose nature or meaning cannot be made out, followed in 1531, in Elyot's Governour, and was used of people and their looks from 1718.^[7] Shakespeare used it in 1600, in The Merchant of Venice, of a person closed to moral appeals.^[7] In physics, from 1666 in Boyle, an impenetrable body is one that no other body can occupy at the same time.^[7][11] Johnson (1755) defined it as "not to be pierced" and "impervious".^[12]

Timeline

• 1447 – impossible to penetrate or enter.^[9][5]
• 1531 – of things, impossible to understand or fathom.^[7]
• 1600 – closed to ideas or moral influence.^[7]
• 1666 – in physics, having impenetrability.^[7]
• 1718 – of people, inscrutable.^[7]

Meanings

Adjective

1. Impossible to get into, through or pierce: a thicket impenetrable to all but the deer.^[11][2][7]
2. Impossible to understand; incomprehensible or inscrutable: an impenetrable legal contract.^[11][7]
3. Impossible to see through: an impenetrable fog.^[11]
4. Not moved by ideas, reason or feeling: a heart impenetrable to pity.^[11][2][7]
5. (physics) Of a body, unable to occupy the same space as another body.^[11][7]

Word family

• impenetrableness
• impenetrably

Related words

• penetrable
• penetrate
• impenetrability

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
3. ^ a b c Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
4. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
5. ^ a b c d Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
6. ^ Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
7. ^ 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
8. ^ a b c Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
9. ^ a b c d 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)
10. ^ a b Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
11. ^ a b c d e f Collins English Dictionary (2023), Glasgow: HarperCollins
12. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.