Onion Knight is a Job from Final Fantasy Tactics: The War of the Lions. One of the new Jobs, the Onion Knight has very basic stats, and no real abilities. It has hidden potential, in that it has increased power dependent on the amount of other Jobs the unit has mastered, much like Freelancers in other games, like Final Fantasy V.
To get one level, the character must master two Jobs, so to get the maximum Onion Knight level the character must master fourteen Jobs. However, mastering the Squire, Chemist, Mime, or Dark Knight Job will not count towards leveling up an Onion Knight.
The Onion Knight learns no abilities. It is also unable to equip any abilities of any kind. Onion Knights' special ability is that they are able to use any kind of equipment, and being the only job class to equip the famed Onion Equipment.