unknown unknown

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English[edit]

Etymology[edit]

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

Noun[edit]

unknown unknown (plural unknown unknowns)

  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.
    • 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:
      This means there are technical unknowns, unknown unknowns, and technical uncertainties in the contract.
    • 2014 January 29, Kenneth Chang, “Beings not made for space: After years of missions, health problems of astronauts elude doctors”, in International New York Times[1], page 7:
      NASA officials often talk about the "unknown unknowns" – the unforeseen problems that catch them by surprise.

Synonyms[edit]

Related terms[edit]