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?

[…] a hen teaches this language with equal ease to the ducklings, she has hatched from suppositious eggs, and educates as her own offspring […]

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

Look, Dr. Lanning, let me present you with a suppositious case. Supposing we had a politician who was interested in defeating a reform candidate at any cost and while investigating his private life came across oddities such as I have just mentioned.