means A large celestial body that orbits a star, is massive enough to be round, and has cleared its orbital neighborhood of other debris.

from From Greek 'planetes,' meaning 'wanderer' — because to ancient sky-watchers these bright points drifted against the fixed backdrop of stars instead of staying put like everything else. The Greeks called them 'asteres planetai,' wandering stars. The word came into English through Latin 'planeta' and Old French, long before anyone knew these wanderers were worlds in their own right.