Definitions of burden:

• noun:   an onerous or difficult concern

  Example: "The burden of responsibility"

• noun:   the central idea that is expanded in a document or discourse
• noun:   weight to be borne or conveyed
• noun:   the central meaning or theme of a speech or literary work
• verb:   weight down with a load
• verb:   impose a task upon, assign a responsibility to
• name:  A surname (common: 1 in 20000 families; popularity rank in the U.S.: #2327)