Nihlum, also known as the Void Moon, is one of three natural satellites orbiting the world of Arbitron. Unlike the other two moons (Vernum and Indicum), Nihlum does not reflect sunlight, and so it appears in the night sky as a black void, blotting out the stars behind it.

Nihlum only appears in the night sky three times a year, and it only appears with Vernum and Indicum once a year.