1. 作为“信封”（最常见用法）
She sealed the letter in an envelope.
她把信装进信封并封好。
The invitation came in a beautifully designed envelope.
邀请函装在一个设计精美的信封里。
2. 表示“包裹、覆盖”（动词用法）
Mist enveloped the entire valley at dawn.
黎明时分，薄雾笼罩了整个山谷。
Darkness quickly enveloped the city after sunset.
日落后，黑暗迅速笼罩了城市。
3. 技术/比喻用法：“极限范围”或“包络线”
The aircraft pushed the performance envelope during the test flight.
这架飞机在试飞中突破了性能极限。
His ideas were outside the traditional envelope of political thought.
他的想法超出了传统政治思想的范畴。
4. 日常实用短语
He handed me a white envelope with cash inside.
他递给我一个装着现金的白色信封。
Don’t forget to write your return address on the envelope.
别忘了在信封上写上你的回邮地址。