What does the word sure mean?

Usage examples for sure

  1. " No," said the other, " I'm not sure, but I know. – At Sunwich Port, Complete by W.W. Jacobs
  2. Sure, there's nothin' we can do! – The Finding of Haldgren by Charles Willard Diffin
  3. Sure of that, now? – Our World, or, The Slaveholders Daughter by F. Colburn Adams