The Collaborative International Dictionary of English v.0.48:

Similitude \Si*mil"i*tude\, n. [F. similitude, L. similitudo,
   from similis similar. See Similar.]
   1. The quality or state of being similar or like;
      resemblance; likeness; similarity; as, similitude of
      substance. --Chaucer.
      [1913 Webster]

            Let us make now man in our image, man
            In our similitude.                    --Milton.
      [1913 Webster]

            If fate some future bard shall join
            In sad similitude of griefs to mine.  --Pope.
      [1913 Webster]

   2. The act of likening, or that which likens, one thing to
      another; fanciful or imaginative comparison; a simile.
      [1913 Webster]

            Tasso, in his similitudes, never departed from the
            woods; that is, all his comparisons were taken from
            the country.                          --Dryden.
      [1913 Webster]

   3. That which is like or similar; a representation,
      semblance, or copy; a facsimile.
      [1913 Webster]

            Man should wed his similitude.        --Chaucer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

similitude
    n 1: similarity in appearance or character or nature between
         persons or things; "man created God in his own likeness"
         [syn: likeness, alikeness, similitude] [ant:
         dissimilitude, unlikeness]
    2: a duplicate copy [syn: counterpart, similitude, twin]