- existing only in the imagination or fancy; not real; fancied: an imaginary illness; the imaginary animals in the stories of Dr. Seuss.
noun, plural im·ag·i·nar·ies.
- Mathematics. imaginary number.
- existing in the imagination; unreal; illusory
- maths involving or containing imaginary numbers. The imaginary part of a complex number, z, is usually written Im z