The Collaborative International Dictionary of English v.0.48:

Superpose \Su`per*pose"\, v. t. [imp. & p. p. Superposed; p.
   pr. & vb. n. Superposing.] [F. superposer. See Super-,
   and Pose.]
   1. To lay upon, as one kind of rock on another.
      [1913 Webster]

   2. (Geom.) To lay (a figure) upon another in such a manner
      that all the parts of the one coincide with the parts of
      the other; as, to superpose one plane figure on another.
      [1913 Webster]

WordNet (r) 3.0 (2006):

superpose
    v 1: place (one geometric figure) upon another so that their
         perimeters coincide
    2: place on top of; "can you superimpose the two images?" [syn:
       superimpose, superpose, lay over]