unknown unknown
unknown unknown noun: 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.
Noun
unknown unknown (plural unknown unknowns)
- 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.
- This means there are technical unknowns, unknown unknowns, and technical uncertainties in the contract.1970, United States Congress. Senate. Committee on the Judiciary. Subcommittee on Antitrust and Monopoly, Competition in Defense Procurement – 1969: Hearing, Ninety-first Congress, page 166
- Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the...2002 February 12, Donald Rumsfeld, “Defense.gov News Transcript: DoD News Briefing – Secretary Rumsfeld and Gen. Myers, United States Department of Defense (defense.gov)”, in Defense.gov Transcript...
- Synonyms:
- unk-unk
Examples of unknown unknown in a sentence
- But there are also unknown unknowns—the ones we don't know we don't know.2002 February 12, Donald Rumsfeld, “Defense.gov News Transcript: DoD News Briefing – Secretary Rumsfeld and Gen. Myers, United States...
- NASA officials often talk about the "unknown unknowns" – the unforeseen problems that catch them by surprise.2014 January 29, Kenneth Chang, “Beings not made for space: After years of missions, health problems of astronauts elude doctors”, in...
- But there are far more unknown unknowns.2026 April 15, Christian Wolmar, “Public deserve answers on overdue HS2 reset”, in RAIL, number 1059, page 45:
Synonyms of unknown unknown
Forms of unknown unknown
| plural | unknown unknowns |
|---|
Origin of unknown unknown
Popularized by Donald Rumsfeld in 2002, though used much earlier.
Questions about unknown unknown
- What does unknown unknown mean?
- Unknown unknown means 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.
- How do you use unknown unknown in a sentence?
- But there are also unknown unknowns—the ones we don't know we don't know.
- What part of speech is unknown unknown?
- Unknown unknown is a noun.
- What is the plural of unknown unknown?
- The plural of unknown unknown is unknown unknowns.
Words near unknown unknown in the dictionary
Source and license
Adapted from Wiktionary: unknown unknown (page history and authors). Text available under the Creative Commons Attribution-ShareAlike 4.0 license. Word.ws reformatted the entry and added links. Wiktionary data of 2026-09-02.
Last updated:
Cite this entry: “unknown unknown.” Word.ws, https://word.ws/unknown_unknown. Based on Wiktionary, CC BY-SA 4.0.