The answer is an envelope. It contains a letter.
The word is "envelope" (which usually holds only one letter).
It does
Envelope is a noun.
on the envelope.
The prepositional phrase in the sentence is "on the envelope".
This envelope is like the window envelope,but the window opening is uncovered (an uncovered address panel).
The possessive form for the noun envelope is envelope's.Example: The envelope's flap wasn't sealed.
When sending a wedding invitation the response card should go into the response envelope and you should address it back to you on the front of the response envelope with a stamp on the envelope.
I opened the envelope that contained my check.
Envelopes is correct.
When addressing a standard envelope, the correct location for the return address is the upper left corner of the envelope.