1. Someone who serves as a sailor, or who navigates or assists in navigating a ship; a seaman: Tom's uncle was a mariner who spent most of his life on a vessel travelling the oceans of the world.
2. In aerospace, one of a series of U.S. space probes that obtained scientific information while flying by or orbiting around specific planets: The Mariner is described as a series of solar-powered probes of Venus, Mars, and Mercury that were launched by NASA between 1962 and 1973 and which provided the first close-up television pictures of another planet (Venus).