spoonsful
That's puzzling.
voldemort
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.
The word possibly is an 8-letter word that contains the letter B.
Clippers (LA)
envelopeAn envelope usually contains only one letter.
FEEDBACK
boldface, feedback
therein
Inimical comes to mind, but I'm sure there are others. I can do you one letter better: a 7 letter word that contains three Is is "idiotic".
stir
dessert