imaginary expression

from The Collaborative International Dictionary of English v.0.48
Imaginary \Im*ag"i*na*ry\, a. [L. imaginarius: cf. F.
   imaginaire.]
   Existing only in imagination or fancy; not real; fancied;
   visionary; ideal.
   [1913 Webster]

         Wilt thou add to all the griefs I suffer
         Imaginary ills and fancied tortures?     --Addison.
   [1913 Webster]

   {Imaginary calculus} See under {Calculus}.

   {Imaginary expression} or {Imaginary quantity} (Alg.), an
      algebraic expression which involves the impossible
      operation of taking the square root of a negative
      quantity; as, [root]-9, a + b [root]-1.

   {Imaginary points}, {lines}, {surfaces}, etc. (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.

   Syn: Ideal; fanciful; chimerical; visionary; fancied; unreal;
        illusive.
        [1913 Webster]