zwitterion, n.

zwitterion
http://www.oed.com/dictionary/zwitterion_n%3Ftab%3Dmeaning_and_use
First published 1986; not fully revised

# zwitterionnoun

## Earlier version

- zwitterion in OED Second Edition (1989)

## Factsheet

### What does the noun zwitterion mean?

There is one meaning in OED's entry for the noun zwitterion. See ‘Meaning & use’ for definition, usage, and quotation evidence.

#### Entry status

OED is undergoing a continuous programme of revision to modernize and improve definitions. This entry has not yet been fully revised.

### How common is the noun zwitterion?

About 0.06occurrences per million words in modern written English

1920 | 0.037
1930 | 0.044
1940 | 0.049
1950 | 0.052
1960 | 0.061
1970 | 0.06
1980 | 0.061
1990 | 0.061
2000 | 0.059
2010 | 0.055

### How is the noun zwitterion pronounced?

#### British English

/ˈtsvɪtəˌrʌɪən/
TSVIT-uh-righ-uhn
/ˈzwɪtəˌrʌɪən/
ZWIT-uh-righ-uhn

#### U.S. English

/ˈtsvɪdəˌraɪən/
TSVID-uh-righ-uhn
/ˈtsvɪdəˌraɪˌɑn/
TSVID-uh-righ-ahn

### Where does the noun zwitterion come from?

Earliest known use

1900s

The earliest known use of the noun zwitterion is in the 1900s.

OED's earliest evidence for zwitterion is from 1906, in the writing of G. Mann.

zwitterion is a borrowing from German.

Etymons: German zwitter-ion.

### Nearby entries

1. zuur-veldt, n. 1785–
2. zuz, n. 1688–
3. zwanziger, n. 1828–
4. Zweig, n. 1973–
5. zwieback, n. 1894–
6. zwieselite, n. 1861–
7. Zwinglian, n. & adj. 1532–
8. Zwinglianism, n. 1581–
9. Zwinglianist, n. 1673–1759
10. zwischenzug, n. 1941–
11. zwitterion, n.1906–
12. zwitterionic, adj. 1946–
13. Zydeco, n. 1949–
14. zygadite, n. 1861–
15. zygaena, n. 1717–
16. zygaenid, n. & adj. 1913–
17. zygaenidan, n. 1837–
18. zygal, adj. 1886–
19. zygantrum, n. 1854–
20. zygapophysial, adj. 1870–
21. zygapophysis, n. 1854–

## Etymology

### Summary

A borrowing from German.
Etymon: German zwitter-ion.
< German zwitter-ion (F. W. Küster 1897, in Zeitschr. f. anorg. Chem. XIII. 136), < zwitter hermaphrodite, hybrid (Old High German zwitar(a)n, < zwi- twi- comb. form) + ion ion n.

## Meaning & use

Chemistry.

1. 1906–
   A molecule or ion having separate positively and negatively charged atoms or groups.
   1. 1906

      > Ions which are simultaneously electro-positive and electro-negative (Bredig), and which Küster calls ‘Zwitter-ions’, i.e. hermaphrodite-ions. Thus the ‘Zwitter-ion’ of glycocoll is the group H3N—CH2—COO.

      G. Mann, Chemistry of Proteids vi. 210
   2. 1925

      > The ‘isomeric change’ now takes the form of a fission of the molecule by the rupture of a bond, the final ionisation of which provides the electric charges which are needed to neutralise those already present in the ‘Zwitterion’.

      Journal of Chemical Society vol. 127 1381
   3. 1937

      > One of the greatest advances in the understanding of the physico~chemical behaviour of amino-acids and proteins is due to the zwitterion theory introduced by Bjerrum in 1923.

      Nature 18 September 492/1
   4. 1948

      > The products of [penicillin] inactivation are zwitter-ions.

      Endeavour vol. 7 85/2
   5. 1949

      > The penicilloic acids are zwitterions with two acid groups and one basic group.

      E. Chain in H. W. Florey et al., Antibiotics vol. II. xxii. 847
   6. 1968

      > At the pH of living cells, lecithin forms a balanced zwitterion.

      D. W. Wood, Principles of Animal Physiology iii. 35
   7. 1982

      > It is useful to calculate the exact pH at which an amino acid is electrically neutral and in its zwitterion form.

      R. M. Schultz in T. M. Devlin, Textbook of Biochemistry ii. 41
   chemistry
   1. zwitterion 1906–
      A molecule or ion having separate positively and negatively charged atoms or groups.
   View in Historical Thesaurus

## Pronunciation

### British English

/ˈtsvɪtəˌrʌɪən/
TSVIT-uh-righ-uhn
/ˈzwɪtəˌrʌɪən/
ZWIT-uh-righ-uhn

### U.S. English

/ˈtsvɪdəˌraɪən/
TSVID-uh-righ-uhn
/ˈtsvɪdəˌraɪˌɑn/
TSVID-uh-righ-ahn
/ˈzwɪdəˌraɪən/
ZWID-uh-righ-uhn
/ˈzwɪdəˌraɪˌɑn/
ZWID-uh-righ-ahn

####

##### Consonants

- ppea
- ttea
- kkey
- bbuy
- ddye
- ɡguy
- tʃchore
- dʒjay
- ffore
- θthaw
- ssore
- ʃshore
- vvee
- ðthee
- zzee
- ʒbeige
- xloch
- hhay
- llay
- ɬrhingyll
- rray
- wway
- jyore
- mmay
- nnay
- ŋsing

Some consonants can take the function of the vowel in unstressed syllables. Where necessary, a syllabic marker diacritic is used, hence /ˈpɛtl/ but /ˈpɛtl̩i/.

##### Vowels

- iːfleece
- ihappy
- ɪkit
- ɛdress
- atrap, bath
- ɑːstart, palm, bath
- ɒlot
- ɔːthought, force
- ʌstrut
- ʊfoot
- uːgoose
- əletter
- əːnurse
- ɪənear
- ɛːsquare
- ʊəcure
- eɪface
- ʌɪpride
- aʊmouth
- əʊgoat
- ɔɪvoice
- ãgratin
- ɒ̃salon
- ᵻ(/ɪ/-/ə/)
- ᵿ(/ʊ/-/ə/)

##### Other symbols

- The symbol ˈ at the beginning of a syllable indicates that that syllable is pronounced with primary stress.
- The symbol ˌ at the beginning of a syllable indicates that that syllable is pronounced with secondary stress.
- Round brackets ( ) in a transcription indicate that the symbol within the brackets is optional.

View the pronunciation model here.

####

##### Consonants

- ppea
- ttea
- kkey
- bbuy
- ddye*
- ɡguy
- tʃchore
- dʒjay
- ffore
- θthaw
- ssore
- ʃshore
- vvee
- ðthee
- zzee
- ʒbeige
- xloch
- hhay
- llay
- rray
- wway
- jyore
- mmay
- nnay
- ŋsing

* /d/ also represents a 'tapped' /t/ as in

Some consonants can take the function of the vowel in unstressed syllables. Where necessary, a syllabic marker diacritic is used, hence /ˈpɛd(ə)l/ but /ˈpɛdl̩i/.

##### Vowels

- ifleece, happy
- ɪkit
- ɛdress
- ætrap, bath
- ɑlot, palm, cloth, thought
- ɑrstart
- ɔcloth, thought
- ɔrnorth, force
- ʊfoot
- ugoose
- əstrut, comma
- ərnurse, letter
- ɪ(ə)rnear
- ɛ(ə)rsquare
- ʊ(ə)rcure
- eɪface
- aɪpride
- aʊmouth
- oʊgoat
- ɔɪvoice
- ɑ̃gratin
- æ̃salon
- ᵻ(/ɪ/-/ə/)
- ᵿ(/ʊ/-/ə/)

##### Other symbols

- The symbol ˈ at the beginning of a syllable indicates that that syllable is pronounced with primary stress.
- The symbol ˌ at the beginning of a syllable indicates that that syllable is pronounced with secondary stress.
- Round brackets ( ) in a transcription indicate that the symbol within the brackets is optional.

View the pronunciation model here.

####

Simple text respell breaks words into syllables, separated by a hyphen. The syllable which carries the primary stress is written in capital letters. This key covers both British and U.S. English Simple Text Respell.

##### Consonants

b, d, f, h, k, l, m, n, p, r, s, t, v, w and z have their standard English values

- gguy
- jjay
- yyore
- chchore
- khloch
- shshore
- ththaw
- dhthee
- zhbeige

##### Vowels

- atrap
- ahpalm
- airsquare
- arstart
- arrcarry (British only)
- awthought
- ayface
- a(ng)gratin
- edress
- eefleece
- eerdeer
- errmerry
- ikit
- ighpride
- irrmirror
- olot (British only)
- ohgoat
- oogoose
- oorcure
- orforce
- orrsorry (British only)
- owmouth
- oyvoice
- o(ng)salon
- ustrut
- uhletter
- urnurse
- urrhurry
- uufoot

## Forms

### Variant forms

Formerly also zwitter-ion and with capital initial.

## Frequency

zwitterion typically occurs about 0.06 times per million words in modern written English.

zwitterion is in frequency band 3, which contains words occurring between 0.01 and 0.1 times per million words in modern written English. More about OED's frequency bands

Frequency data is computed programmatically, and should be regarded as an estimate.

### Frequency of zwitterion, n., 1920–2010

* Occurrences per million words in written English

Historical frequency series are derived from Google Books Ngrams (version 2), a data set based on the Google Books corpus of several million books printed in English between 1500 and 2010.

The overall frequency for a given word is calculated by summing frequencies for the main form of the word, any plural or inflected forms, and any major spelling variations.

For sets of homographs (distinct entries that share the same word-form, e.g. mole, n.¹, mole, n.², mole, n.³, etc.), we have estimated the frequency of each homograph entry as a fraction of the total Ngrams frequency for the word-form. This may result in inaccuracies.

Smoothing has been applied to series for lower-frequency words, using a moving-average algorithm. This reduces short-term fluctuations, which may be produced by variability in the content of the Google Books corpus.

Decade | Frequency per million words
--- | ---
1920 | 0.037
1930 | 0.044
1940 | 0.049
1950 | 0.052
1960 | 0.061
1970 | 0.06
1980 | 0.061
1990 | 0.061
2000 | 0.059
2010 | 0.055

### Frequency of zwitterion, n., 2017–2024

* Occurrences per million words in written English

Modern frequency series are derived from a corpus of 20 billion words, covering the period from 2017 to the present. The corpus is mainly compiled from online news sources, and covers all major varieties of World English.

Smoothing has been applied to series for lower-frequency words, using a moving-average algorithm. This reduces short-term fluctuations, which may be produced by variability in the content of the corpus.

Period | Frequency per million words
--- | ---
2017 | 0.001
2018 | 0.0007
2019 | 0.004
2020 | 0.0047
2021 | 0.0073
2022 | 0.011
2023 | 0.013
2024 | 0.012

## Compounds & derived words

Sort by

1. zwitterionic, adj. 1946–

zwitterion, n. was first published in 1986; not fully revised.

zwitterion, n. was last modified in March 2025.