# xi

> English word · Noun · IPA /zaɪ/ · frequency rank #5,928

## Definitions
1. The 14th letter of Classical and Modern Greek. The 15th in Ancient and Old Greek.
2. Either of a pair of hyperons having spin 1/2, which decay into a lambda particle and a pion.

## Etymology
From Ancient Greek ξεῖ (xeî), ξῖ (xî).

## Easily confused with
- **XL** (https://plainspell.com/en/vs/xi-vs-xl)
- **XP** (https://plainspell.com/en/vs/xi-vs-xp)
- **XO** (https://plainspell.com/en/vs/xi-vs-xo)
- **XM** (https://plainspell.com/en/vs/xi-vs-xm)
- **Xt** (https://plainspell.com/en/vs/xi-vs-xt)
- **XR** (https://plainspell.com/en/vs/xi-vs-xr)
- **XXX** (https://plainspell.com/en/vs/xi-vs-xxx)
- **XML** (https://plainspell.com/en/vs/xi-vs-xml)
- **Xie** (https://plainspell.com/en/vs/xi-vs-xie)
- **XYZ** (https://plainspell.com/en/vs/xi-vs-xyz)
- **Xin** (https://plainspell.com/en/vs/xi-vs-xin)
- **Xia** (https://plainspell.com/en/vs/xi-vs-xia)
- **XPS** (https://plainspell.com/en/vs/xi-vs-xps)
- **Xue** (https://plainspell.com/en/vs/xi-vs-xue)
- **xiao** (https://plainspell.com/en/vs/xi-vs-xiao)
- **Xian** (https://plainspell.com/en/vs/xi-vs-xian)
- **xing** (https://plainspell.com/en/vs/xi-vs-xing)
- **X** (https://plainspell.com/en/vs/x-vs-xi)
- **XC** (https://plainspell.com/en/vs/xc-vs-xi)
- **xe** (https://plainspell.com/en/vs/xe-vs-xi)

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