Definitions of damn:

• noun:   something of little value

  Example: "His promise is not worth a damn"

• verb:   wish harm upon; invoke evil upon
• adjective:   used as expletives

  Example: "Oh, damn (or goddamn)!"

• adjective:   expletives used informally as intensifiers

  Example: "I'll be damned (or blessed or darned or goddamned) if I'll do any such thing"

• adverb:   extremely