Definition of "envelope" []

• A flat paper container, especially for a letter, usually having a gummed flap. (noun)
• Something that envelops; a wrapping. (noun)
• Biology An enclosing structure or cover, such as a membrane or the outer coat of a virus. (noun)
• The bag containing the gas in a balloon or airship. (noun)
• The set of limitations within which a technological system, especially an aircraft, can perform safely and effectively. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Note: The roots of the term envelope generator and its basic functionality are described in "Envelopes" on page 626."
• "Though Mr. Talbot has cut off all communication between the sisters, a cryptic letter from Lilian manages to slip through, and hidden in the envelope is a puzzling photograph of a tiger hunt."
• "Make sure that the gap you used to turn the envelope is at the top left."