This power (page 199 of into the storm) says that while active attacks against the psyker treat him as if he had the holy trait.

Does anyone know what this actually means? I cant find any mention of the holy trait in the rogue trader books, the closest thing I can think of is acting as if the psykers armour is hexagramicly warded.

Anyone know for sure?

It's the inverse of the Daemonic Trait, I believe. So, double your Toughness bonus against any weapon with the Warp Weapon Trait. I can't find it in any of the books though, Dark Heresy or otherwise. .