improbable vs likely

improbable

adj
  • Not likely to be true. 

  • Not likely to happen. 

likely

adj
  • probable; having a greater-than-even chance of occurring 

  • Reasonably to be expected; apparently destined, probable 

  • attractive; pleasant 

  • appropriate, suitable; believable; promising, having a good potential 

  • plausible; within the realm of credibility 

  • leading with high probability to some specified outcome 

adv
  • Probably. 

noun
  • Something or somebody considered likely. 

How often have the words improbable and likely occurred in a corpus of books? (source: Google Ngram Viewer )