fissile

Etymology

It is borrowed from Latin fissilis (“that may be split”),^{[2][3][4][5][6]} from fissus (“split”), the past participle of findō (“to cleave, split”),^[3][4][7][8] with the suffix -ilis.^[6][9] Etymonline traces the verb to Proto-Indo-European *bheid- (“to split”),^[3] and Klein relates it to Old English bītan (“to bite”), the source of bite.^[4] The OED compares French fissile.^[2] Fission and fissure go back to the same Latin stem.^[5]

Earliest recorded meaning

Able to be split, or tending to split: 1661, in R. Lovell's Panzōoryktologia.^[2][6] Etymonline likewise dates the word to the 1660s,^[3] and Dictionary.com to 1655–65.^[9]

Semantic evolution

For nearly three centuries the word belonged mainly to the description of materials that split along a grain or along planes of cleavage, such as wood and crystals.^[6] Johnson (1755) defined it as having a grain that lets a thing be cleft, and quoted it of a crystal.^[10] The American Heritage Dictionary lists a geological use, of rock that splits easily along close parallel planes.^[11] The Shorter Oxford quotes the word figuratively of the Labour Party.^[7] In 1945, in Nature, it was taken up in nuclear physics for material that can undergo fission,^[2] sometimes specifically fission by slow neutrons.^[2][12] The noun fissility is recorded from the late 17th century.^[7]

Timeline

• 1661 – able to be split, tending to split.^[2][6]
• 1945 – able to undergo nuclear fission.^[2]

Meanings

Adjective

1. Able to be split, or tending to split, as wood along the grain or a crystal along planes of cleavage: a fissile slate.^[6][2][12]
2. (geology) Easily split along close parallel planes.^[11]
3. (physics) Able to undergo nuclear fission; fissionable.^{[11][6][2][12]}

Word family

• fissility
• nonfissile
• unfissile

Related words

• fission
• fissure
• fissionable
• bite
• bifid

Usage notes

Collins records a difference of use: in British English fissile is applied to material that undergoes fission on the impact of slow neutrons, while in American and Canadian English it is simply another word for fissionable.^[12] The American Heritage Dictionary, by contrast, glosses the physics sense as fissionable especially by neutrons of all energies.^[11]

References

1. ^ 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 Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
5. ^ a b Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
6. ^ a b c d e f g Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
7. ^ a b c Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
8. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
9. ^ a b Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
10. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
11. ^ a b c d The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
12. ^ a b c d Collins English Dictionary (2023), Glasgow: HarperCollins