可数名词：

1. 信封；封皮，封套

2. 包裹物，包装物；覆盖物；套，罩

3. 外表；外(机)壳，外层，壳层

4.【航空学】(飞船或飞艇的)蒙皮；(飞船、飞艇或气球的)气囊

5.（特定飞机或系统等的）极限数据，（飞行）速度极限

6.【生物学】包袋，膜；【植物学】包被；围绕部分(如花冠)

7.【几何学】包迹，包络线；包络面

8.【电信学】包络(曲)线

9.【天文学】包层

英语解释

a curve that is tangent to each of a family of curves

the maximum operating capability of a system

any wrapper or covering

the bag containing the gas in a balloon

a natural covering (as by a fluid)

a flat rectangular paper container for papers