The Collaborative International Dictionary of English v.0.48:

Encasement \En*case"ment\, n. [Cf. Casement.]
   1. The act of encasing; also, that which encases.
      [1913 Webster]

   2. (Biol.) An old theory of generation similar to
      embo[^i]tement. See Ovulist.
      [1913 Webster]

WordNet (r) 3.0 (2006):

encasement
    n 1: the act of enclosing something in a case [syn:
         encasement, incasement]