envelope
noun
[ ˈɛnvələʊp ]
• a flat paper container with a sealable flap, used to enclose a letter or document.
• a covering or containing structure or layer.
• "the external envelope of the swimming pool"
Origin:
mid 16th century (in the sense ‘wrapper, enveloping layer’; originally as envelope ): from French enveloppe, from envelopper ‘envelop’. The sense ‘covering of a letter’ dates from the early 18th century.
push the envelope
• approach or extend the limits of what is possible.
• "these are extremely witty and clever stories that consistently push the envelope of TV comedy"
