Webster's Revised Unabridged Dictionary · 1913

Imaginary

Imaginary , adjective

[Latin imaginarius: compare French 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
Collocations (3)
Imaginary calculus , See under Calculus.
Imaginary expression or Imaginary quantity (Algebra) , an algebraic expression which involves the impossible operation of taking the square root of a negative quantity; as, r-9, a + b r-1.
Imaginary points or lines or surfaces (Geometry) , 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.

Imaginary , noun

(Algebra) An imaginary expression or quantity.