Android, PC
Permafrost and frigid accuity are the names of the runes.

What those runes do is boost ice mastery (as well as magic resist for permafrost). So, you're right, they are pretty similar :D.
Keep in mind you must have the primary rune, Frigid on hat, Perma on Chest Armor. The runes on any other armor or accessory etc is a bonus to those 2. If you don't have the rune on armor or hat, you don't get the bonuses from other perma/frigid runes.