envelope

The word “envelope” means a flat paper or cardboard cover used to hold and mail letters or documents. In plain terms, a paper wrapper for a letter — or, more abstractly, the outer boundary of what's safely possible.

“Envelope” is pronounced EHN-vuh-lohp (/ˈɛnvə(ˌ)loʊp/ in IPA).

Here is “envelope” used in a sentence: “She sealed the invitation inside a cream-colored envelope.”

Depending on how it is used, “envelope” can be a noun and a verb.

The word “envelope” comes from French. From French enveloppe. The "safe operating limits" sense grew out of the aviation phrase "flight envelope.".

“Envelope” is a fairly common word in modern English, usually learned at around the A2 level.

“Envelope” has 3 distinct senses listed in this dictionary. The most common is: a flat paper or cardboard cover used to hold and mail letters or documents.

In everyday use, an envelope is the paper cover used to mail letters and documents. In aviation and engineering, a "flight envelope" refers to the outer limits within which an aircraft or system can operate safely, such as maximum speed or altitude. The two senses share the idea of a boundary or covering but apply to very different contexts.

This idiom comes from the technical meaning of envelope as the safe operating limits of a system, especially an aircraft. To push the envelope means to test or exceed normal boundaries of what is considered safe or acceptable, extending performance or behavior beyond established limits.

Yes, as a verb it means to wrap something up completely, enclosing it on all sides. This usage is far less common than the noun form and is often confused with the closely related word "envelop," which is the standard spelling for the verb in modern English.