Hidden Spell
Masks the aura of spells with durations longer than instantaneous.
When you cast a spell with a duration longer than instantaneous, you can spend 2 sorcery points to mask its magical aura. For the duration of your spell, it can’t be detected or discerned with spells or effects, such as the detect magic spell or a chuul’s Sense Magic trait.
Source and licence
From Tome of Heroes.
Licence: Open Game Content (OGL 1.0a).