Super*impo*si"tion

from The Collaborative International Dictionary of English v.0.48

Superimpose \Su`per*im*pose"\, v. t. [imp. & p. p.
   {Superimposed}; p. pr. & vb. n. {Superimposing}.]
   To lay or impose on something else; as, a stratum of earth
   superimposed on another stratum. -- {Su`per*im`po*si"tion},
   n.
   [1913 Webster]