The Collaborative International Dictionary of English v.0.48:

Italicize \I*tal"i*cize\, v. t. & i. [imp. & p. p. Italicized;
   p. pr. & vb. n. Italicizing.]
   To print in Italic characters; to underline written letters
   or words with a single line; as, to Italicize a word;
   Italicizes too much.
   [1913 Webster]

WordNet (r) 3.0 (2006):

italicize
    v 1: print in italics [syn: italicize, italicise]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "italicize":
   accent, accentuate, belabor, dwell on, emphasize, feature,
   give emphasis to, harp on, highlight, overaccentuate,
   overemphasize, overstress, place emphasis on, play up, point up,
   punctuate, rub in, spotlight, star, stress, underline,
   underscore