adverb (r)

• definitely or positively (`sure' is sometimes used informally for `surely')(adv.all)

  Example:
  The results are surely encouraging.
  

  Synonym:
  certainly, for certain, for sure, sure, sure as shooting, sure enough
  

  source: wordnet30
• In a sure or certain manner; certainly; infallibly; undoubtedly; assuredly.(adverb)

  source: webster1913