Existing only as a concept.
not based on fact; dubious; "the falsehood about some fanciful secret treaties"- F.D.Roosevelt; "a small child's imaginary friends"; "her imagined fame"; "to create a notional world for oneself"
indulging in or influenced by fancy; "a fanciful mind"; "all the notional vagaries of childhood"
being (or being of the nature of) a notion or concept; "a plan abstract and conceptional"; "to improve notional comprehension"; "a notional response to the question"