envelope

US /ˈɑːn.və.loʊp/
UK /ˈɑːn.və.loʊp/
"envelope" picture
1.

信封

a flat, usually square or rectangular, paper container with a gummed flap, used for enclosing a letter or document

:
She sealed the letter in an envelope.
她把信封在信封里。
Please put the documents in a large envelope.
请把文件放在一个大信封里。
2.

包膜, 外壳

a layer or surrounding part that encloses or covers something

:
The planet is surrounded by a thick gaseous envelope.
这颗行星被一层厚厚的气体包围着。
The virus has a protective protein envelope.
该病毒具有保护性蛋白质包膜