improbable

Adjective

• too improbable to admit of belief
  • a tall story
    

• having a probability too low to inspire belief

• not likely to be true or to occur or to have occurred
  • legislation on the question is highly unlikely
    
  • an improbable event
    

Related words

• Synonyms: 
  marvelous , marvellous , tall(a) , unbelievable , unconvincing , unlikely
• Antonyms: 
  probable , likely