From Planet X
1. A flat, folded paper container, especially for a letter. 2. Something that envelops; a wrapping. 3. An enclosing structure or cover, such as a membrane or the outer coat of a virus. 4. The bag containing the gas in a balloon or an airship. 5. The set of limitations within which a technological system, especially an aircraft, can perform safely and effectively. 6. The coma of a comet. 7. A curve or surface that is tangent to every one of a family of curves or surfaces. 8. To increase the operating capabilities of a technological system.