imaginary

(noun) (mathematics) a number of the form a+bi where a and b are real numbers and i is the square root of -1. Synonyms: complex number, complex quantity, imaginary number.

(adj) not based on fact; unreal. Synonyms: fanciful, notional. Examples: "The falsehood about some fanciful secret treaties"- f.d.roosevelt." "A small child's imaginary friends." "To create a notional world for oneself."