envelopes
n. countable A2 Elementary US //ˈɛnvəˌɫoʊps// en·velopes
n. flat paper containers used for sending letters or documents. You slide the paper inside and seal the top before mailing it.
n. flat, rectangular paper containers with a sealable flap, designed to enclose letters or documents for postage.
I need to buy some envelopes for these letters.
She carefully addressed the white envelopes before placing the wedding invitations inside and sealing them with a sticker.
The archive contains hundreds of hand-addressed envelopes, many of which still bear the original wax seals and postmarks from the early nineteenth century.
Usage
Commonly used in the plural when referring to stationery supplies.