Source : Webster's Revised Unabridged Dictionary (1913)

Imaginary \Im*ag"i*na*ry\, a. [L. imaginarius: cf. F.
   imaginaire.]
   Existing only in imagination or fancy; not real; fancied;
   visionary; ideal.

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

   {Imaginary calculus} See under {Calculus}.

   {Imaginary expression} or {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.

Imaginary \Im*ag"i*na*ry\, n. (Alg.)
   An imaginary expression or quantity.

Source : WordNet®

imaginary
     adj : not based on fact; dubious; "the falsehood about some
           fanciful secret treaties"- F.D.Roosevelt; "a small
           child's imaginary friends"; "her imagined fame"; "to
           create a notional world for oneself" [syn: {fanciful},
           {imagined}, {notional}]