unknown quantity

plural unknown quantities

1. idiomaticA person or thing whose nature or value is a mystery.

   [H]e was still an unknown quantity – a young, untested figure.

   2015 December 6, “Congratulations on 10 years, David Cameron - but don't rest on your laurels”, in Telegraph, UK, retrieved 09 Jan 2016

   5 more examples

   Whatever he had learned of himself was here of no avail. He was an unknown quantity.

   1895 October, Stephen Crane, chapter I, in The Red Badge of Courage: An Episode of the American Civil War, New York, N.Y.: D[aniel] Appleton and Company, →OCLC, page 14

   . . . the Evening Post of this city to refer to him recently as "the young Belgian painter," and to the general public he is an unknown quantity.

   1907, The Bookman, volume 25, page 166

   The big French diesel is something of an unknown quantity, whereas many French-built electric locomotives developing 3,000 h.p. and more have been well proved in service.

   1963 June, “Beyond the Channel: France: High-power diesels”, in Modern Railways, page 417

   In spite of more than three decades of public service, I knew I was an unknown quantity to many of my countrymen and to much of the world when I assumed office.

   1971, Lyndon Johnson, “"I feel like I have already been here a year"”, in The Vantage Point, Holt, Reinhart & Winston, →ISBN, →LCCN, →OCLC, page 18

   Amin Gemayel, it is felt here, is an unknown quantity and it is impossible to predict how he will act.

   1982 September 22, Henry Tanner, “Gemayel Brothers Assessed in Syria”, in New York Times, retrieved 09 Jan 2016

   Antonyms: known quantity, household name

2. Used other than figuratively or idiomatically: see unknown, quantity.

   So promising was the Skunk Works' stealth cruise missile offering, the USAF ordered an unknown quantity of these missiles under a highly classified program dubbed Senior Prom.

   2016, Steve Pace, The Projects of Skunk Works: 75 Years of Lockheed Martin's Advanced Development Programs, Voyageur Press, →ISBN, page 145

   1 more example

   Many of the applications of mathematics require that you identify an unknown quantity, assign a variable to that quantity, and then attempt to express another unknown quantity in terms of that variable.

   2012 January 1, Richard N. Aufmann, Joanne Lockwood, Beginning Algebra, Cengage Learning, →ISBN, page 77

   Synonyms: blank canvas, enigma