Source : Webster's Revised Unabridged Dictionary (1913)

Envelopment \En*vel"op*ment\, n. [Cf. F. enveloppement.]
   1. The act of enveloping or wrapping; an inclosing or
      covering on all sides.

   2. That which envelops or surrounds; an envelop.

Source : WordNet®

envelopment
     n : the act of enclosing something inside something else [syn: {enclosure},
          {enclosing}, {inclosure}]