Lux Arumque

So, I just came back from Vespers from my local Unitarian Universalist Church, and the had a hymn called Lux Arumque by Eric Whitacre. I puzzled what the "arum" was. ("altar"--the closest I could think of-- didn't seem to make sense, in multiple ways) Supposedly it is "gold"? Is that ecclesiastical latin for "aurum"? When googling, even one of the titles for a piece talking about the hymn was "Lux Aurumque".