The Collaborative International Dictionary of English v.0.48:

emphasis \em"pha*sis\ ([e^]m"f[.a]*s[i^]s), n.; pl. Emphases
   ([e^]m"f[.a]*s[=e]z). [L., fr. Gr. 'e`mfasis significance,
   force of expression, fr. 'emfai`nein to show in, indicate;
   'en in + fai`nein to show. See In, and Phase.]
   1. (Rhet.) A particular stress of utterance, or force of
      voice, given in reading and speaking to one or more words
      whose signification the speaker intends to impress
      specially upon his audience.
      [1913 Webster]

            The province of emphasis is so much more important
            than accent, that the customary seat of the latter
            is changed, when the claims of emphasis require it.
                                                  --E. Porter.
      [1913 Webster]

   2. A peculiar impressiveness of expression or weight of
      thought; vivid representation, enforcing assent; as, to
      dwell on a subject with great emphasis.
      [1913 Webster]

            External objects stand before us . . . in all the
            life and emphasis of extension, figure, and color.
                                                  --Sir W.
                                                  Hamilton.
      [1913 Webster]

   3. a special attention given to, or extra importance attached
      to, something; as, a guided tour of Egypt with emphasis on
      the monuments along the Nile.
      [PJC]

   4. something to which great importance is attached; as, the
      need for increased spending on education was the emphasis
      of his speech.
      [PJC]

WordNet (r) 3.0 (2006):

emphasis
    n 1: special importance or significance; "the red light gave the
         central figure increased emphasis"; "the room was decorated
         in shades of grey with distinctive red accents" [syn:
         emphasis, accent]
    2: intensity or forcefulness of expression; "the vehemence of
       his denial"; "his emphasis on civil rights" [syn:
       vehemence, emphasis]
    3: special and significant stress by means of position or
       repetition e.g.
    4: the relative prominence of a syllable or musical note
       (especially with regard to stress or pitch); "he put the
       stress on the wrong syllable" [syn: stress, emphasis,
       accent]