The Collaborative International Dictionary of English v.0.48:

Emphasize \Em"pha*size\, v. t. [imp. & p. p. Emphasized; p.
   pr. & vb. n. Emphasizing.]
   To utter or pronounce with a particular stress of voice; to
   make emphatic; as, to emphasize a word or a phrase.

WordNet (r) 3.0 (2006):

emphasize
    v 1: to stress, single out as important; "Dr. Jones emphasizes
         exercise in addition to a change in diet" [syn: stress,
         emphasize, emphasise, punctuate, accent,
         accentuate]
    2: give extra weight to (a communication); "Her gesture
       emphasized her words" [syn: underscore, underline,
       emphasize, emphasise]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "emphasize":
   accent, accentuate, assert, bear down on, belabor,
   call attention to, charge, dwell on, feature, give emphasis to,
   harp on, highlight, italicize, mark, overaccentuate, overemphasize,
   overstress, pinpoint, place emphasis on, play up, point up, press,
   punctuate, rub in, spotlight, star, stress, underline,
   underscore