Source : Webster's Revised Unabridged Dictionary (1913)

Emphasis \Em"pha*sis\, n.; pl. {Emphases}. [L., fr. Gr. ?
   significance, force of expression, fr. ? to show in,
   indicate; ? in + ? 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.

            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.

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

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

Source : WordNet®

emphasis
     n 1: special importance or significance; "the red light gave the
          central figure increased emphasis"; "the room was
          decorated in shades of gray with distinctive red
          accents" [syn: {accent}]
     2: intensity or forcefulness of expression; "the vehemence of
        his denial"; "his emphasis on civil rights" [syn: {vehemence}]
     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}, {accent}]
     [also: {emphases} (pl)]