Supposititious, a.
Etymology: [L. suppositicus. See Supposition.]
1. Fraudulently substituted for something else; not being what is purports to be; not genuine; spurious; counterfeit; as, a supposititious child; a supposititious writing. Bacon.
2. Suppositional; hypothetical. [R.] Woodward. -- Sup*pos`i*ti"tious*ly, adv. -- Sup*pos`i*ti"tious*ness, n.
Shades of meaning
Fernald lists supposititious only as an antonym, under real.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given