I know it's Latin.
Also yes, Tenebrous Tunnels... funny how it led to the Black Garden, where either a Hive Worm or a shard of the Darkness was laid to rest.
Idea 1: Maybe, and this is a thought. Remember when the vex over ran the hive when The idiot known as Crota opened up a portal and how they found the dark heart when they came into this universe. Maybe it’s something related to the dark heart. But that is just speculation.
Idea 2: Perchance it is something to old houses when the Traveler went to the home planet of the Eliskens (the fallen) and some negative byproduct it created when it gave the gift of light to the Fallen. Either way, it will relate to the Travelers past and or creation.