unknown quantities

Noun

unknown quantity (plural unknown quantities)

1. (idiomatic) A person or thing whose nature or value is a mystery.
   • 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

   Antonyms:

   known quantity, household name

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