Why "an envelop" doesn’t work: a grammar breakdown
What kind of error is it?

Spelling and grammatical error
Why do people make this mistake?
People often confuse "envelop" (a verb meaning to wrap or surround something) with "envelope" (a noun referring to a flat paper container for letters). This mistake can come from the similar pronunciation and the fact that the words are spelled nearly the same.
What is correct?
The correct form is "envelope" for the noun (a container for letters) and "envelop" for the verb (which means to surround or enclose).
Examples of correct usage
- a letter in an envelope
- Please envelop the package.
- I need an envelope for the card.
- The fog began to envelop the city.