Imaginary means existing only in the mind, and not in the real world. An imaginary friend, an imaginary line, imaginary fears.
An imaginary friend is a normal part of childhood and is linked with better social understanding rather than loneliness. In mathematics an imaginary number is a real and useful thing despite the name — it is the square root of a negative number.
1adjectiveimaginaryExisting only in the mind.
“The equator is an imaginary line around the middle of the earth.”
imaginary is a quality of unreality.
Latin imaginarius comes from imago, an image or likeness. Image and imagine are the same root.
Latin
imāginārius — relating to images, fancied
Middle English
ymaginarie
English, today
imaginary
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.
Etymology from Wiktionary, CC BY-SA