Envelope is the answer.
The eight-letter word you are looking for is "envelope." It contains one letter (as in a piece of mail) inside it, while also being eight letters long.
envelope
Envelope.
Double-u
Eight is Light
Landlord is an eight letter word for innkeeper.
Eight letter word is "response"
one word LUDEN"S
One choice is the word peculiar.
An eight letter word with x as a second letter is exciting.
envelopeAn envelope usually contains only one letter.
An eight letter word for wealthy is affluent.