envelope
UK: ˈɛnvələʊp | US: ˈɑːnvəloʊp
n. a flat paper container used to enclose a letter or document
n. a covering or outer layer, especially one that encloses something
n. (mathematics) a curve or surface tangent to a family of curves or surfaces
The word "envelope" entered English in the early 18th century from French "enveloppe," which originally meant "a wrapping." It combines the prefix "en-" (in) with the root "velop" (wrap), reflecting the action of enclosing something within a folded cover. The Latin root "volvere" (to roll) hints at the earlier idea of rolling or folding materials for protection, later evolving into the flat paper container we know today.
She sealed the letter inside a white envelope.
The spacecraft’s heat envelope protects it during re-entry.
Please address the envelope clearly before mailing it.
The artist used an envelope of light to create a dreamy effect.
The envelope of sound from the speakers filled the room.