Dictionary:

supposititious

  (sə-pŏz'ĭ-tĭsh'əs)

1. Substituted with fraudulent intent; spurious.
2. Hypothetical; supposed. See synonyms at supposed.

[From Latin suppositīcius, from suppositus, past participle of suppōnere, to substitute. See suppose.]

adjective

1. Fraudulently or deceptively imitative: bogus, counterfeit, fake, false, fraudulent, phony, sham, spurious, suppositious. See true/false.
2. Presumed to be true, real, or genuine, especially on inconclusive grounds: conjectural, hypothetic, hypothetical, inferential, presumptive, supposed, suppositional, suppositious, suppositive. See belief/unbelief.

The adjective has one meaning:

Meaning #1: based primarily on surmise rather than adequate evidence
  Synonyms: conjectural, supposed, suppositional, suppositious