from The American Heritage® Dictionary of the English Language, 5th Edition.

  • adjective Having existence only in the imagination; unreal.
  • adjective Of or being the coefficient of the imaginary unit in a complex number.
  • adjective Of, involving, or being an imaginary number.
  • adjective Involving only a complex number of which the real part is zero.
  • noun An imaginary number.

from The Century Dictionary.

  • Existing only in imagination or fancy; due to erroneous belief or conception; not real; baseless; fancied: opposed to actual.
  • In mathematics, unreal and feigned in accordance with the theory of imaginary quantities.
  • Synonyms Ideal, fanciful, fancied, visionary, unreal, shadowy, Utopian. Imaginary and imaginative are never synonymous: imaginary means existing only in the imagination; imaginative means possessed of or showing an active imagination.
  • noun In algebra, an imaginary expression or quantity.

from the GNU version of the Collaborative International Dictionary of English.

  • adjective Existing only in imagination or fancy; not real; fancied; visionary; ideal.
  • adjective See under Calculus.
  • adjective (Alg.) an algebraic expression which involves the impossible operation of taking the square root of a negative quantity; as, √-9, a + b √-1.
  • adjective (Geom.) points, lines, surfaces, etc., imagined to exist, although by reason of certain changes of a figure they have in fact ceased to have a real existence.
  • noun (Alg.) An imaginary expression or quantity.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective existing only in the imagination
  • adjective mathematics of a number, having no real part; that part of a complex number which is a multiple of the square root of -1.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adjective not based on fact; unreal
  • noun (mathematics) a number of the form a+bi where a and b are real numbers and i is the square root of -1


from Wiktionary, Creative Commons Attribution/Share-Alike License

From Latin imāginārius ("relating to images, fancied"), from imāgo.


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  • Imagine a comment.

    November 5, 2007

  • The auto-generated definition is mathematically correct for a complex number, though in common usage it also applies to an imaginary number. The mathematically correct definition for imaginary number is:

    (n): (mathematics) a number of the form "bi" where "b" is a real number and i is the square root of -1

    May 13, 2008

  • Saturn is the only planet in our solar system that is less dense than water. If you could build an imaginary gigantic bathtub, Saturn would float in it.

    National Geographic, trying to palm it off on NASA. No, if you built an imaginary bath, the water would still all fall through. You need to imagine building a real gigantic bath for this one.

    February 23, 2009

  • That's really not such a great analogy if you think about it too much. I'm pretty sure the gravitational pull of Saturn would do some things do a bathtub full of water. The whole idea of floating doesn't make a lot of sense on this scale.

    March 2, 2009

  • And in fact the water would have to be a cuboidal volume sufficient to contain a hemisphere of Saturn, and that's got some gravity of its own (that's an emphatic 'some' . . . I wonder how you punctuate that?); not to mention the rigid material for the bath.

    March 2, 2009

  • Well, it can be done; it just takes some imagination.

    The revery alone will do…

    March 2, 2009