More than one functional section can be included in a single envelope; a dual triode configuration is particularly common.

Once you have completed the nomination application, please send all materials together in a single envelope, to the following address:

The manager opens the safety deposit box and Kate takes the contents inside: a single envelope.

But what they both witnessed was an empty safe, except for a single envelope sealed with red wax.

The prosecution produced as evidence a single empty envelope which it claimed contained the brochure.

They had been placed in a single envelope and sealed.

Mark riffled the edge of the pack and saw that not a single envelope had been opened.

For years, the holiday would slip by without my addressing a single envelope.

She opened the pouch, which was now full-fleshed, and pulled out the single envelope within.

Without a single envelope being opened, Oscar's verdict is already in.