envelope /ˈenvələʊp/ noun [C] WORKPLACE
› a flat, usually square or rectangular, paper container for a letter: a brown/manila envelope a sealed envelope
› a flat, usually square or rectangular, plastic container used for keeping papers in: The papers were handed to me in a transparent plastic envelope.
push the envelope › to go further than the usual limits by doing something new, dangerous, etc.: We're really pushing the envelope on this technology; a lot of other companies are just playing catch-up. → See also padded envelope, pre-paid envelope, self-addressed envelope, self-addressed stamped envelope, stamped addressed envelope