It Swings Backwards and Forwards Beneath Clocks
Puzzle 18 of Happy Hour Piece of Cake Pack
Question is: It Swings Backwards and Forwards Beneath Clocks
and the answer is: PENDULUM
Word Meaning:
PENDULUM — (clocks, mechanics) A body suspended from a fixed support so that it swings freely back and forth under the influence of gravity, commonly used to regulate various devices such as clocks.
Definitions from Wiktionary.