envelope vs gasbag

envelope and gasbag both are nouns.

Word	Noun	Adjective	Verb	Adverb
envelope	Yes	No	No	No
gasbag	Yes	No	No	No

As nouns, envelope and gasbag are synonyms defined as:

envelope (noun)	gasbag (noun)
any wrapper or covering	the bag containing the gas in a balloon
a flat (usually rectangular) container for a letter, thin package, etc.	a boring person who talks a great deal about uninteresting topics
the bag containing the gas in a balloon
the maximum operating capability of a system (especially an aircraft)
a natural covering (as by a fluid)
a curve that is tangent to each of a family of curves