Jet Ski (jĕt) A trademark for a personal watercraft. Jet Ski. n (Swimming, Water Sports & Surfing) trademark a small self-propelled vehicle for one person resembling a scooter, which skims across water on a flat keel, and is steered by means of handlebars. vb (intr; usually not capitals) , -skis, -skiing, -skied or-ski'd (Swimming, Water Sports & Surfing) to ride a Jet Ski. Jet Skier n. Jet Skiing n. Jet′ Ski` Trademark. a jet-propelled boat ridden like a motorcycle.