fission

Etymology

It is borrowed from Latin fissiō (“a cleaving, a splitting”),^{[2][3][4][5][6]} a noun of action from fissus (“split”), the past participle of findō (“to split”).^[3][6][7][8] Barnhart thinks the borrowing was perhaps helped by the older English word fissure.^[4] Etymonline and Webster's New World trace the Latin verb to Proto-Indo-European *bheid- (“to split”), the root of Old English bītan (“to bite”) and so of bite.^[3][8][7]

Earliest recorded meaning

The action of splitting or breaking into parts: Merriam-Webster dates this sense to about 1617,^[7] and the Shorter Oxford and the Oxford Dictionary of English put the word in the early 17th century,^[9][10] though the Shorter Oxford notes that it was rare before the mid-19th century.^[9] The OED's earliest quotation is from 1846, in the biological sense,^[2] which Etymonline dates to 1819^[3] and Barnhart to 1841.^[4]

Semantic evolution

The word was taken up in 19th-century biology for the splitting of a cell or organism into new ones as a way of reproducing.^[2][3][4] Astronomers used it from 1919 for the supposed breaking up of one star into two,^[2] and in 1939 Meitner and Frisch applied it, in Nature, to the splitting of a heavy atomic nucleus,^[2] the sense that is now the most familiar.^[3][4][11] A verb, to split or to undergo fission, was formed from the noun in 1929;^[2][4][3] it has been used of nuclei in physics since 1947,^[2] and the adjective fissionable followed in 1945.^[4]

Timeline

• c. 1617 – the action of splitting or dividing into parts.^[7][9] The OED's first quotation for this sense is from 1865.^[2]
• 1819 – the division of a cell or organism as a means of reproduction.^[3] The OED's first record is from 1846, and Barnhart's from 1841.^[2][4]
• 1919 – in astronomy, the supposed splitting of one star into two.^[2]
• 1929 – verb, to split or divide.^[2][4][7]
• 1939 – the splitting of a heavy atomic nucleus.^[2][3][4]
• 1945 – fissionable, able to undergo nuclear fission.^[4]
• 1947 – verb, of nuclei, to split, or to cause to split.^[2]

Meanings

Noun

1. The act or process of splitting or breaking up into parts: the fission of the party into rival factions.^[11][7][2]
2. (biology) A form of asexual reproduction in which a cell or single-celled organism divides into two or more new ones.^[11][2][9]
3. (physics) Nuclear fission: the splitting of a heavy atomic nucleus into lighter nuclei, which releases energy.^[11][2][9]

Verb

1. To undergo fission, or to cause something to undergo it.^[7][2][9]

Word family

• fissional
• fissile
• fissionable
• photofission
• fission bomb
• nuclear fission
• binary fission

Related words

• fissure
• fusion
• bite

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 o p q Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f g h i Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e f g h i j k Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
5. ^ The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
6. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
7. ^ a b c d e f g Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
8. ^ a b Webster's New World College Dictionary (2014), 5th ed., Boston: Houghton Mifflin Harcourt
9. ^ a b c d e f Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
10. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
11. ^ a b c d Collins English Dictionary (2023), Glasgow: HarperCollins