# cysteine

> English word · Noun · IPA /ˈsɪs.təˌiːn/ · frequency rank #43,590

## Definitions
1. A sulphur-containing nonessential amino acid C₃H₇NO₂S found in most animal proteins; it readily oxidizes to cystine.

## Etymology
An alteration of cystine, see -eine.

## Common misspellings (12)
`ccysteine`, `csyteine`, `cysetine`, `cyssteine`, `cysteien`, `cysteinne`, `cystenie`, `cystiene`, `cystteine`, `cytseine`, `cyysteine`, `ycsteine`

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/cysteine