dwarf planet
noun [ C ] uk/ˈdwɔːf ˌplæn.ɪt/ us/ˈdwɔːrf ˌplæn.ɪt/
矮行星
a round mass of metal and rock or gas, moving around the Sun or another star, that is not large enough to be considered a planet. Dwarf planets in the solar system include Ceres, Pluto, and Eris.