Preveiling is the act of preemptively casting Holy Veil on yourself or others before the player becomes hexed. Purifying Veil may also be used, though it is less common.
Removing Holy Veil/Purifying Veil is a lot faster than casting a hex removal skill, and thus an important Hex can quickly be removed. This quick removal is very useful when facing foes who cover their more dangerous hexes with spells like Parasitic Bond, because you are able to remove the first hex before the second one is applied.
Hexes commonly preveiled against include:
Purifying Veil is most effective against Daze.