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]

Moby Thesaurus II by Grady Ward, 1.0:

132 Moby Thesaurus words for "emphasis":
   Alexandrine, accent, accentuation, amphibrach, amphimacer,
   anacrusis, anapest, antispast, arsis, attention, bacchius, beat,
   cadence, caesura, catalexis, chloriamb, chloriambus, colon,
   concern, concernment, consequence, consequentiality, consideration,
   counterpoint, cretic, dactyl, dactylic hexameter, diaeresis,
   dimeter, dipody, dochmiac, elegiac, elegiac couplet,
   elegiac pentameter, epitrite, excellence, feminine caesura, foot,
   force, grammatical accent, gravity, heptameter, heptapody,
   heroic couplet, hexameter, hexapody, high order, high rank, iamb,
   iambic, iambic pentameter, ictus, import, importance, interest,
   intonation, intonation pattern, ionic, jingle, level of stress,
   lilt, mark, masculine caesura, materiality, measure, merit, meter,
   metrical accent, metrical foot, metrical group, metrical unit,
   metrics, metron, molossus, moment, mora, movement, note, numbers,
   paeon, paralipsis, paramountcy, pentameter, pentapody, period,
   pitch accent, precedence, preeminence, primacy, primary stress,
   priority, proceleusmatic, prominence, prosodics, prosody, pyrrhic,
   quantity, rhetorical accent, rhythm, rhythmic pattern,
   rhythmical accent, rhythmical stress, secondary stress,
   self-importance, significance, spondee, sprung rhythm, stress,
   stress accent, stress arsis, stress pattern, superiority,
   supremacy, swing, syzygy, tertiary stress, tetrameter, tetrapody,
   tetraseme, thesis, tone accent, tribrach, trimeter, tripody,
   triseme, trochee, underlining, underscoring, value, weak stress,
   weight, worth