Old Gateau's name in both English and Japanese is a pun based on the location it is found. In English, the French word gateau ("cake") plays on Chateau. In Japanese, the Chateau's name is "Forest Manor" (Japanese: もりのようかん) while the Gateau's name is "Forest Yōkan" (Japanese: もりのヨウカン); the two terms are homophones and are pronounced as mori no yōkan.
According to the anime, the Old Gateau is also known as the "Mirage Gateau".
In the games, "Old Gateau" is usually pluralized as "Old Gateaux". However, the description of the Souvenir Set in Join Avenue says "A set of two Old Gateaus. The cake heals all the status problems of one Pokémon."