imaginary

Meanings

1. 1
   adj

   Existing only in the mind, not real.

   As a child, she had an imaginary friend she talked to every day.

2. 2
   adj

   In mathematics, relating to a number that is a multiple of the square root of minus one.

   In advanced maths, students learn about imaginary numbers.

3. 3
   noun

   In mathematics, a number of the form a+bi involving the square root of minus one.

   The equation had no real solutions, only imaginaries.

From Middle English ymaginarie, ymagynary, from Latin imāginārius (“relating to images, fancied”), from imāgō, equivalent to imagine + -ary. 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. Although Descartes' usage was derogatory, the designation stuck even after the concept gained acceptance in the 18th century.

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