Curse of Immutability
Items enchanted with curse of immutability will have their enchantments locked in. While a grindstone will still rid the item of any enchantments, except curses, adding enchantments or upgrading enchantments through an anvil is not possible.
Any equipment obtained through villager trading will be cursed with this enchantment, as part of the server rebalances. It is also present on any naturally occuring charged silk touch pickaxe.