adverb (r)

• with considerable certainty; without much doubt(adv.all)

  Example:
  He is probably out of the country.
  

  Synonym:
  belike, in all likelihood, in all probability, likely
  

  source: wordnet30
• easy to believe on the basis of available evidence(adv.all)

  Example:
  He will probably win the election.
  

  Synonym:
  believably, credibly, plausibly
  Antonym:
  implausibly, improbably, incredibly, unbelievably
  

  source: wordnet30
• In a probable manner; in likelihood.(adverb)

  source: webster1913