Placed on Each Side of a Shelf to Prevent Falls
Puzzle 7 of Countdown to 2020 Piece of Cake Pack
Question is: Placed on Each Side of a Shelf to Prevent Falls
and the answer is: BOOKEND
Word Meaning:
BOOKEND — A heavy object or moveable support placed at one or both ends of a row of books for the purpose of keeping them upright.
Definitions from Wiktionary.