The Collaborative International Dictionary of English v.0.48:

Rebus \Re"bus\, v. t.
   To mark or indicate by a rebus.
   [1913 Webster]

         He [John Morton] had a fair library rebused with More
         in text and Tun under it.                --Fuller.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rebus \Re"bus\ (r[=e]"b[u^]s), n.; pl. Rebuses
   (r[=e]"b[u^]s*[e^]z). [L. rebus by things, abl. pl. of res a
   thing: cf. F. r['e]bus. Cf. 3d Real.]
   1. A mode of expressing words and phrases by pictures of
      objects whose names resemble those words, or the syllables
      of which they are composed; enigmatical representation of
      words by figures; hence, a peculiar form of riddle made up
      of such representations.
      [1913 Webster]

   Note: A gallant, in love with a woman named Rose Hill, had,
         embroidered on his gown, a rose, a hill, an eye, a
         loaf, and a well, signifying, Rose Hill I love well.
         [1913 Webster]

   2. (Her.) A pictorial suggestion on a coat of arms of the
      name of the person to whom it belongs. See Canting arms,
      under Canting.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rebus
    n 1: a puzzle where you decode a message consisting of pictures
         representing syllables and words