imaginary

From Middle English ymaginarie, ymagynary, from Latin imāginārius (“relating to images, fancied”), from imāgō.

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.[1] Although Descartes' usage was derogatory, the designation stuck even after the concept gained acceptance in the 18th century.

• (Received Pronunciation) IPA^(key): /ɪˈmædʒɪn(ə)ɹi/
• (General American) IPA^(key): /ɪˈmæd͡ʒɪˌnɛɹi/

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imaginary (comparative more imaginary, superlative most 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 79426475, 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 ${\displaystyle {\sqrt {-1}}}$ (called imaginary unit).

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

imaginary (plural imaginaries)

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

   • 2015, Adrian Daub, Elisabeth Krimmer, Goethe Yearbook 22, page 96:

     While Oil, its extraction, and the global petroculture and its role in transforming the planet's climate undoubtedly play a crucial role in the Antropocene imaginary — to the extent that petrofiction has been construed not just a a genre but as a periodizing gesture of "petromodernity" — it would hamper both the imagination and the root of petrofiction to restrict the range of this term to the encounter with fossil fuels within a carbon imaginary.

2. (mathematics) An imaginary quantity. [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.