implausible (adj.)

• absurd
• debatable
• doubtable
• doubtful
• dubious
• dubitable
• fishy
• flimsy
• improbable
• inconceivable
• incredible
• preposterous
• problematic
• puzzling
• questionable
• ridiculous
• suspect
• suspicious
• tall
• thick
• thin
• unbelievable
• unconvincing
• unearthly
• ungodly
• unimaginable
• unlikely
• unpromising
• unreasonable
• unsubstantial
• unthinkable
• weak