The word planet reflects old scientific theories surprisingly well. It first appeared in Old English as planete, and this was a loanword from the Old French term planete, ultimately from the Late Latin word planeta, mostly used to discuss any celestial body with a path of its own. The word shifts back to planete as we travel back to Greek, and here it gets interesting. Planete was actually the shortening of a phrase, asterea planetai, which literally meant "wandering stars" (since that's how the Greeks differentiated planets: by movement). We've already discovered where aster came from, in the post about "astronaut", bit planetai was the part meaning "wandering", and originally came from the word planesthai, also "wandering". There ate two main theories as to what happens when we move further back: planesthai may have originated from the Proto-Indo-European term pel, meaning "to roam", or, more whimsically, from the Proto-Indo-European term pele, which meant "flat" and would have figuratively meant "to spread around". If the latter is true, then we can truly say our planet is "flat"!
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd