1. (adj)complex number, complex quantity, imaginary number, imaginary (mathematics) a number of the form a+bi where a and b are realnumbers and i is the squareroot of -1
2. (adj)fanciful, imaginary, notional not based on fact; unreal "the falsehood about some fanciful secret treaties"- F.D.Roosevelt; "a small child's imaginary friends"; "to create a notional world for oneself"