1. (noun) the bag containing the gas in a balloon

• gasbag

1. (noun) a flat (usually rectangular) container for a letter, thin package, etc.

• container

2. (noun) any wrapper or covering

• wrap
• wrapper
• wrapping

3. (noun) a curve that is tangent to each of a family of curves

• curve
• curved shape

4. (noun) a natural covering (as by a fluid)

• cover
• covering
• natural covering

5. (noun) the maximum operating capability of a system (especially an aircraft)

• operating capability
• performance capability

6. (noun) the bag containing the gas in a balloon

• bag

1. (noun) a flat (usually rectangular) container for a letter, thin package, etc.

• window envelope