groundless (adj.)

• baseless
• bottomless
• chimerical
• empty
• flimsy
• gratuitous
• hypothetical
• idle
• illusory
• imaginary
• inconclusive
• indecisive
• speculative
• suppositional
• tenuous
• uncalled-for
• uncertified
• unconfirmed
• uncorroborated
• undetermined
• unestablished
• unfixed
• unfounded
• unjustifiable
• unjustified
• unproved
• unproven
• unreasonable
• unsettled
• unsound
• unsubstantiated
• unsupportable
• unsupported
• untenable
• untested
• untried
• unverified
• unwarranted
• vain