From the facebook page :
The keyword "Cantrip" allows the spell to be placed back in your Spellbook if it is destroyed.
Ah yes, I meant I am curious to see what this new type of card does to the game, not what the trait meant. So far I've only seen the Cantrip trait on two cards, both of them Mage specific. Might not be a common trait?
Thank you though, Preacher!