# SI vs su

> English confusable word pair

## The two words

### SI
*name · frequency rank #5,453*
International System of Units

### su
*noun · frequency rank #8,094*
Alternative form of xu (“former Vietnamese currency”).

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