improbable improbable /ˌɪmˈprɑːbəbəl/

adjective

1. () Not likely to be true or to occur or to have occurred  ( improbable , unlikely )
   not likely to be true or to occur or to have occurred
    Legislation on the question is highly unlikely
   legislation on the question is highly unlikely
    An improbable event
   an improbable event
   
2. Too improbable to admit of belief  ( improbable , marvellous [Canadian, British] , tall , marvelous [American] )
   too improbable to admit of belief
    A tall story
   a tall story
   
3. Having a probability too low to inspire belief  ( improbable , unbelievable , unconvincing , unlikely )
   having a probability too low to inspire belief