[ˈɒnv(ə)ləʊp], (Noun)

Definitions:
- a flat paper container with a sealable flap, used to enclose a letter or document

- a covering or containing structure or layer
(e.g: the external envelope of the swimming pool)


Phrases:
- push the envelope
- the back of an envelope

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