Envelope/ˈenvələʊp,ˈɑːnvələʊp/ Definition 1 of 5Pro Tip 1/2Physical Object Think of 'envelope' as a tangible item for containing and protecting documents. She decorated the envelope with stickers before sending it. Pro Tip 2/2Mailing Use Remember 'envelope' is commonly used for letters and cards, especially in a postal context. Post offices sell envelopes of various sizes.