adjective

based on or involving conjecture.

the evidence was deemed too conjectural

speculative,suppositional,theoretical,hypothetical,putative,academic,notional,abstract,postulated,based on guesswork,inferred,suspected,presumed,assumed,presupposed,tentative,unproven,untested,unfounded,groundless,unsubstantiated,ideational,suppositious,suppositive,postulational