Riddle?

The clue on today's Jumble is:

WHAT WORD STARTS AND
ENDS IN 'E' AND CAN HAVE 
JUST ONE LETTER IN IT?

ENVELOPE would satisfy the riddle, but it didn't have enough letters to fill the available space. I found a word that satisfied the on-line version of the puzzle, but I don't understand how it relates to this riddle, if it does at all. The answer to the puzzle is RESERVATIONS (Highlight to read).