The term RUNNER USAIN is a reference to Usain BOLT, the Jamaican sprinter who is widely considered to be the fastest man in the world. The crossword solution for this term is BOLT, which is a four letter word. BOLT is an eight-time Olympic gold medalist and holds the world record in the 100 and 200 meter sprints. He is also the only man to win three consecutive Olympic gold medals in the 100 meter sprint.