Adjectives

(s)fanciful, imaginary, notionalnot based on fact; existing only in the imagination“the falsehood about some fanciful secret treaties” (F.D.Roosevelt), “a small child's imaginary friends”, “to create a notional world for oneself”
(s)notional, speculativenot based on fact or investigation“a notional figure of cost helps in determining production costs”, “speculative knowledge”
(s)fanciful, notionalindulging in or influenced by fancy“a fanciful mind”, “all the notional vagaries of childhood”
(s)conceptional, ideational, notionalbeing of the nature of a notion or concept“a plan abstract and conceptional”, “to improve notional comprehension”, “a notional response to the question”