en
ve
lope
Plural
envelopes
1
a thin, paper cover in which we put and send a letter
- He wrote the address on the envelope.
- I need to buy some envelopes for my Christmas cards.
- She found an old envelope with photos in it.
- She handed me an envelope with a note inside.
- The envelope contained a surprise birthday card.
2
any wrapper or covering
3
the bag containing the gas in a balloon
Synonyms:
4
the maximum operating capability of a system (especially an aircraft)
5
a natural covering (as by a fluid)
6
a curve that is tangent to each of a family of curves