ionization

Etymology

The OED takes it as formed from English ion + -ization, since it is recorded four years before the verb ionize;^[2][3] Etymonline and Merriam-Webster Unabridged derive it from ionize and -ation,^[4][5] and Merriam-Webster Unabridged classes it as International Scientific Vocabulary.^[5] The noun ion was introduced by Michael Faraday in 1834, at the suggestion of William Whewell,^[4][1] from the ending of anion and cation,^[2][1] which is from Ancient Greek ἰόν (ión, “going”), the neuter present participle of εἶμι (eîmi, “I go”),^[1][4][2] from Proto-Indo-European *ei- (“to go”).^[4][6] Ions were so called because they move towards the electrode of opposite charge.^[4]

Earliest recorded meaning

The state of being in the form of ions, or the process of becoming ionized: 1891, in a paper by G. F. Fitzgerald in the Reports of the British Association for the Advancement of Science.^[2] Etymonline also dates the word to 1891.^[4]

Semantic evolution

The word arose in physics and chemistry for the splitting of atoms or molecules into ions, by chemical reaction, heat, electrical discharge or radiation.^[2][7] From 1905 doctors also used it for iontophoresis, the introduction of a drug into the body by an electric current, a sense now rare.^[2][3] It soon formed technical compounds, such as ionization chamber, an instrument that measures the intensity of radiation.^[3]

Timeline

• 1891 – the formation of ions; the state of being ionized.^[2][4]
• 1905 – in medicine, iontophoresis (now rare).^[2]

Meanings

Noun

1. The process by which an atom or molecule gains or loses electrons and becomes an ion, as a result of a chemical reaction, high temperature, electrical discharge or radiation.^[7][5][2]
2. The state of being ionized: the degree of ionization of the gas.^[5][2]
3. (medicine) Iontophoresis (now rare).^[2][3]

Word family

• photoionization
• autoionization

Related words

• ionize
• ion
• anion
• cation

Usage notes

The British spelling ionisation is also used.^[7][5][3] The OED also has a separate word Ionization, with a capital, meaning the making of something Ionic in form (from 1880), from Ionize, to make Ionic.^[2][4]

References

1. ^ a b c d Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e 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 d e f g h Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
5. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
6. ^ The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
7. ^ a b c Collins English Dictionary (2023), Glasgow: HarperCollins