suppositious
Spurious; substituted for the genuine, counterfeit; fake.
[…] who knowes not how false, how suppositious, the writings and Epistles of the auncient Popes are iustly esteemed?
Imaginary; fictitious, pretended to exist.
At rehearsals the actor tossed an entirely imaginary cloak about his shoulders as though it were heavy brocade, courteously removed a hat made of air, and seriously set out on a suppositious table a non-existent dinner, after sedulously cooking it on a kitchen range that was a chair.
Hypothetical, based on supposition; conjectural.
Near-synonyms: assumed, presumed, presumptive, putative, supposed; apparent, likely
Where it comes from
From New Latin suppositius, from Latin suppositīcius.
Adapted from the Wiktionary entry suppositious (CC BY-SA 4.0).