To envelop means to wrap something up completely or surround it entirely. When fog envelops a city, it wraps around every building and street until you can barely see a few feet ahead. When you envelop yourself in a warm blanket on a cold morning, you're wrapping it around your whole body.

The word suggests complete coverage, like being enclosed or swallowed up by something. Darkness might envelop a room when the lights go out. A hug can envelop someone, surrounding them with warmth and comfort. Scientists might describe how water envelops a sinking object, or how flames envelop a piece of paper.

Notice that envelop (with no “e” at the end) is different from envelope (the paper container for letters). They're related: an envelope envelops a letter by wrapping around it completely. But when you're using the verb, you envelop something. When you need the noun for what holds your mail, that's an envelope.

The word often appears when something spreads out and covers something else entirely: silence enveloping a library, cheers enveloping a stadium after a winning goal, or sleep enveloping you at the end of an exhausting day.