planet/ˋplænIt; ˈplænət or ˈplænIt/n [C]1 a very large round object in space that moves around the sun or another star 行星: Mercury is the smallest planet. 水星是最小的行星。see box at见 SPACE1 方框2 the planet the world 地球﹐世界: the environmental future of the planet 地球环境的未来—planetary adj