/ ˈenvələʊp; ˈɒn-; NAmE ˈenvəloʊp; ˈɑːn-/ noun
1.
a flat paper container used for sending letters in :
writing paper and envelopes
an airmail / padded / prepaid envelope
—see also pay envelope , sae , SASE
2.
a flat container made of plastic for keeping papers in
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IDIOMS
see push verb
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WORD ORIGIN
mid 16th cent. (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 cent.