Supposititious1. (a.) Fraudulently substituted for something else; not being what is purports to be; not genuine; spurious; counterfeit; as, a supposititious child; a supposititious writing.
2. (a.) Suppositional; hypothetical.
Thesaurus Entries
Barmecidal, Barmecide, accounted as, affected, airy, alleged, apocryphal, apparent, apparitional, artificial, assumed, assumptive, autistic, baseborn, bastard, bogus, brummagem, chimeric, chimerical, colorable, colored, conjectural, conjectured, counterfeit, counterfeited, deceptive, deemed, delusional, delusionary, delusive, delusory, dereistic, distorted, dreamlike, dreamy, dressed up, dummy, embellished, embroidered, erroneous, ersatz, factitious, fake, faked, fallacious, FALSE, falsified, fancied, fanciful, fantastic, fatherless, feigned, fictional, fictitious, fictive, garbled, given, granted, hypothetical, illegitimate, illusional, illusionary, illusive, illusory, imaginary, imaginational, imagined, imitation, inferred, junky, make-believe, man-made, misbegotten, misleading, mock, natural, nonexistent, notional, ostensible, perverted, phantasmagoric, phantasmal, phantom, phony, pinchbeck, postulated, postulational, premised, presumed, presumptive, pretended, pseudo, put-on, putative, quasi, queer, reputed, seeming, self-deceptive, self-deluding, self-styled, sham, shoddy, simulated, so-called, soi-disant, specious, spectral, spurious, supposed, suppositional, suppositive, suppository, synthetic, taken for granted, tin, tinsel, titivated, twisted, unactual, unauthentic, understood, unfounded, ungenuine, unnatural, unreal, unsubstantial, visional, visionary, warped