Definition of suppositious in English:

suppositious

Pronunciation /ˌsəpəˈziSHəs/ /ˌsəpəˈzɪʃəs/

adjective

  • Based on assumption rather than fact.

    • ‘most of the evidence is purely suppositious’
    unconfirmed, unsupported, uncorroborated, not backed up by evidence, unverified, unattested, unproven, not validated, untested

Origin

Early 17th century (in the sense ‘supposititious’): partly a contraction of supposititious, reinforced by supposition.