# unknown unknown

> English word · Noun

## Definitions
1. An uncertainty of unknown magnitude, consequence, structure, and probability characteristics, possibly with completely unsuspected existence; something that we don't know that we don't know.

## Etymology
Popularized by Donald Rumsfeld in 2002, though used much earlier.

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