I don't recognize certain things as canon if they have been known as different things in different titles, or if they are in great need of being corrected. Canon only affects things that have been consistently the same while at the same time being sufficiently translated. Megalixir for example. Also original FF7 place names (to some extent) and original ff7 character names (because the mistakes have been adopted officially, god only knows why).
But I certainly won't start reversing entire sections of the translation, or we may as well just play the original game.
Null, to nullify; cancel out. It's the best that can be done, really.
Null was used in FFX as well as other FF titles. Esuna means S-na = S-Null. Poisona is Poison-Null.