unbelievable (adj.)

• absurd
• antic
• doubtable
• doubtful
• dubious
• dubitable
• fanciful
• fantastic
• flimsy
• implausible
• impossible
• improbable
• incomprehensible
• inconceivable
• incredible
• mind-boggling
• preposterous
• problematic
• questionable
• ridiculous
• suspect
• suspicious
• tall
• thick
• thin
• unaccountable
• unconvincing
• unearthly
• unexpected
• ungodly
• unimaginable
• unsubstantial
• unthinkable
• weak