From Middle English ymaginarie, ymagynary, from Latin imāginārius, from imāgō, equivalent to .

The mathematical sense derives from René Descartes's use (of the French imaginaire) in 1637, La Geometrie, to ridicule the notion of regarding non-real roots of polynomials as numbers.

• (RP) IPA: /ɪˈmæd͡ʒɪnəɹi/, /ɪˈmæd͡ʒɪnɹi/
• (America) IPA: /ɪˈmæd͡ʒɪˌnɛɹi/

imaginary

1. Existing only in the imagination.

   Unicorns are imaginary.

   • 1712 (date written), [Joseph] Addison, Cato, a Tragedy. […], London: […] J[acob] Tonson, […], published 1713, →OCLC ↗, Act I, scene iv, page 1 ↗:

     Wilt thou add to all the griefs I suffer / Imaginary ills and fancied tortures?

2. (mathematics, of a number) Having no real part; that part of a complex number which is a multiple of \sqrt{-1} (called imaginary unit).

• (existing only in the imagination) all in one's head

• French: imaginaire
• German: eingebildet, imaginär
• Italian: immaginario
• Portuguese: imaginário
• Russian: вообража́емый
• Spanish: imaginario

• German: imaginär
• Portuguese: imaginário
• Russian: мни́мый
• Spanish: imaginario

imaginary (plural imaginaries)

1. Imagination; fancy. [from 16th c.]
   • 2002, Colin Jones, The Great Nation, Penguin, published 2003, page 324:

     By then too Mozart's opera, from Da Ponte's libretto, had made Figaro a stock character in the European imaginary and set the whole Continent whistling Mozartian airs and chuckling at Figaresque humour.

2. (mathematics) An imaginary number. [from 18th c.]
3. (sociology) The set of values, institutions, laws, and symbols common to a particular social group and the corresponding society through which people imagine their social whole. [from c. 1975]