# upon vs USO

> English confusable word pair

## The two words

### upon
*preposition · IPA /əˈpɒn/ · frequency rank #798*
A higher-register or more formal alternative to on in most, though not all, prepositional uses.

### USO
*noun · frequency rank #35,573*
Unidentified submerged object or unidentified submarine object.

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