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Envelope
01
信封, 封套
a thin, paper cover in which we put and send a letter
Example
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
封套, 包装纸
any wrapper or covering
03
气囊, 气球袋
the bag containing the gas in a balloon
04
外包络, 极限操作能力
the maximum operating capability of a system (especially an aircraft)
05
包围层, 覆盖层
a natural covering (as by a fluid)
06
包络线, 包络曲线
a curve that is tangent to each of a family of curves
