The Seat on a Bicycle
Puzzle 15 of Buying Books Piece of Cake Pack
Question is: The Seat on a Bicycle
and the answer is: SADDLE
Word Meaning:
SADDLE — A seat for a rider, typically made of leather and raised in the front and rear, placed on the back of a horse or other animal, and secured by a strap around the animal's body.
Definitions from Wiktionary.