covering vs envelope

covering and envelope both are nouns.

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

As nouns, envelope is a hyponym of covering; that is, envelope is a word with a more specific, narrower meaning than covering:

covering (noun)	envelope (noun)
the act of protecting something by covering it	any wrapper or covering
the work of applying something	a flat (usually rectangular) container for a letter, thin package, etc.
the act of concealing the existence of something by obstructing the view of it	the bag containing the gas in a balloon
an artifact that covers something else (usually to protect or shelter or conceal it)	the maximum operating capability of a system (especially an aircraft)
a natural object that covers or envelops	a natural covering (as by a fluid)
	a curve that is tangent to each of a family of curves