en·vel·op /ɪnˈvɛləp, ɛn-/
 (vt.)包,裹,封,包圍,裝入信封
 En·vel·ope En·vel·op n.
 1. That which envelops, wraps up, encases, or surrounds; a wrapper; an inclosing cover; esp., the cover or wrapper of a document, as of a letter.
 2. Astron. The nebulous covering of the head or nucleus of a comet; -- called also coma.
 3. Fort. A work of earth, in the form of a single parapet or of a small rampart. It is sometimes raised in the ditch and sometimes beyond it.
 4. Geom. A curve or surface which is tangent to each member of a system of curves or surfaces, the form and position of the members of the system being allowed to vary according to some continuous law. Thus, any curve is the envelope of its tangents.
 push the envelope  to increase the capability of some type of machine or system; -- usually by technological development.
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 En·vel·op v. t. [imp. & p. p. Enveloped p. pr. & vb. n. Enveloping.]  To put a covering about; to wrap up or in; to inclose within a case, wrapper, integument or the like; to surround entirely; as, to envelop goods or a letter; the fog envelops a ship.
    Nocturnal shades this world envelop.   --J. Philips.
 envelop
      v : enclose or enfold completely with or as if with a covering;
          "Fog enveloped the house" [syn: enfold, enwrap, wrap,
           enclose]