What does the word swear mean?

Usage examples for swear

  1. All my people swear by him." – Somewhere in France by Richard Harding Davis
  2. Can you swear it was her? – Caught in a Trap by John C. Hutcheson
  3. He has to be the sort of a man his men will swear by. – The Argus Pheasant by John Charles Beecham