The term 'winter-sport vehicle' can refer to a skibob, which is a six-letter word. A skibob is a type of winter sport vehicle that combines elements of skiing and cycling. It consists of a frame with two skis at the front and a single wheel at the back, and is propelled by the rider pushing against the ground with their feet. Skibobs are used for recreational purposes, such as downhill racing, and can reach speeds of up to 60 mph.