**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]