Cupid= romantic? marksman?
Cupid is a word there is no need to make it one.
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 is the answer.
envelope
Envelope.
Double-u
Eight is Light
one word LUDEN"S
One choice is the word peculiar.
envelopeAn envelope usually contains only one letter.
FIREWORK
There are no six-letter English words that end with "bun." However, there is one eight-letter word: honeybun.