imaginary

From Middle French imaginaire, from Latin imāginārius (“relating to images, fancied”), from imāgō.

The mathematical sense derives from René Descartes's use (of the French imaginaire) in 1673, 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): /ɪˈmædʒɪˌnɛɹi/

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imaginary (comparative more imaginary, superlative most imaginary)

1. Existing only in the imagination.

   Santa Claus is imaginary.

   • Addison

     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 the square root of -1.

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

• imaginarily
• imaginariness
• imaginarity
• imaginary number
• imaginary unit

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.

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.