The Collaborative International Dictionary of English v.0.48:

Advertisement \Ad*ver"tise*ment\ ([a^]d*v[~e]r"t[i^]z*ment or
   [a^]d`v[~e]r*t[imac]z"ment; 277), n. [F. avertisement,
   formerly also spelled advertissement, a warning, giving
   notice, fr. avertir.]
   1. The act of informing or notifying; notification. [Archaic]
      [1913 Webster]

            An advertisement of danger.           --Bp. Burnet.
      [1913 Webster]

   2. Admonition; advice; warning. [Obs.]
      [1913 Webster]

            Therefore give me no counsel:
            My griefs cry louder than advertisement. --Shak.
      [1913 Webster]

   3. A public notice, especially a paid notice in some public
      print; anything that advertises; as, a newspaper
      containing many advertisements.
      [1913 Webster]

WordNet (r) 3.0 (2006):

advertisement
    n 1: a public promotion of some product or service [syn: ad,
         advertisement, advertizement, advertising,
         advertizing, advert]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "advertisement":
   ad, advert, advertising, announcement, ballyhoo, bill, blurb,
   broadcast, broadside, brochure, circular, classified, commercial,
   handbill, hype, notice, placard, plug, poster, proclamation,
   promotion, promulgation, pronouncement, pronunciamento, propaganda,
   publication, publicity, puffery, spot announcement