The Collaborative International Dictionary of English v.0.48:

Headline \Head"line`\ (-l[imac]n`), n.
   1. (Print.) The line at the head or top of a page.
      [1913 Webster]

   2. (Naut.) See Headrope.
      [1913 Webster]

   3. (Journalism) A title for an article in a newspaper,
      sometimes one line, sometimes more, set in larger and
      bolder type than the body of the article and indicating
      the subject matter or content of the article.
      [PJC]

   4. A similar title at the top of the newspaper indicating the
      most important story of the day; also, a title for an
      illustration or picture.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

headline \head"line`\ (-l[imac]n`), v. t.
   1. To mention in a headline.
      [PJC]

   2. To furnish with a headline (senses 1, 3, or 4).
      [PJC]

   3. To publicise prominently in an advertisement.
      [PJC]

WordNet (r) 3.0 (2006):

headline
    n 1: the heading or caption of a newspaper article [syn:
         headline, newspaper headline]
    v 1: publicize widely or highly, as if with a headline
    2: provide (a newspaper page or a story) with a headline