Envelope
01
信封, 封套
a thin, paper cover in which we put and send a letter
例子
He wrote the address on the envelope.
他把地址写在信封上。
I need to buy some envelopes for my Christmas cards.
我需要为我的圣诞卡买一些信封。
02
信封, 包装
any wrapper or covering
03
信封, 气囊
the bag containing the gas in a balloon
04
包络线, 操作上限
the maximum operating capability of a system (especially an aircraft)
05
包膜, 覆盖物
a natural covering (as by a fluid)
06
包络线, 包络
a curve that is tangent to each of a family of curves
