Synonyms for Supposititious (same or very similar meaning)
WordNet sense 1 (based primarily on surmise rather than adequate evidence):
conjectural, hypothetical, supposed, divinatory, hypothetic, suppositional, suppositiousWordNet sense 2 (concerned primarily with theories or hypotheses rather than practical considerations):
theoretic, theoreticalFrom the ODE community, based on WordNetadd/edit