Used in Recipes
Obtained from Desynthesis
How to Obtain
In the Japanese slang "Onion" (the word onion is also used in Japanese like this) also means grutty or cheap.
The starting job in Final Fantasy III is called "Onion Kid," who uses onion weapons. (In the Nintendo DS version of FF3 the Onion Kid is called "Freelancer" and, instead, there is an ultimate job called "Onion Knight").