Useful If You Jump Out of a Plane
Puzzle 19 of Christmas Stockings Hard Pack
Question is: Useful If You Jump Out of a Plane
and the answer is: PARACHUTE
Word Meaning:
PARACHUTE — (aviation) A device, generally constructed from fabric, that is designed to employ air resistance to control the fall of an object or person, causing them to float instead of falling.
Definitions from Wiktionary.