means The sport of jumping from an aircraft and free-falling through the air before opening a parachute to land safely.

from A clean modern compound of "sky" and "diving" — "sky" from Old Norse "ský," meaning cloud, and "dive" from Old English "dūfan," to plunge or sink. The word itself is a 20th-century coinage, born with the sport once parachutes became reliable enough to fall on purpose; before that, people who left planes mid-flight were generally trying very hard not to.