envelope

Where it comes from

Envelope ordinarily means a paper cover for a letter, or another enclosing wrapper. Envelope is the English form of French enveloppe, an enclosing cover. French formed that noun from envelopper, to wrap or cover; the deeper origin of the verb is uncertain. English had already borrowed envelop as a verb centuries before envelope became the familiar noun. Envelope first meant a wrapper or enclosing cover generally and then specifically a prepared wrapper for a letter. The object was named for what it does: it envelops its contents.

How the meaning developed

Later scientific and technical envelopes extended that enclosing image beyond paper.

In use

One is usually a verb. One is a wrapper.
Which fits: She sealed the letter inside an ______?

An “envelope” is a wrapper or covering. To “envelop” is to wrap or surround something completely.
Fog can envelop a town. A letter goes in an envelope.