Adjective unlikely has 3 senses
  1. improbable, unlikely - not likely to be true or to occur or to have occurred; "legislation on the question is highly unlikely"; "an improbable event"
  2. unlikely - has little chance of being the case or coming about; "an unlikely story"; "an unlikely candidate for reelection"; "a butcher is unlikely to preach vegetarianism"
    likely, apt, liable, probable, promising
  3. improbable, unbelievable, unconvincing, unlikely - having a probability to low to inspire belief
    Antonym: plausible (indirect, via implausible)