dark light

Etymology 1
. From being a force found in the dark sector that acts on dark matter, analog to light in the "light sector" (the part of the universe that is not part of the dark sector) that acts on "light matter" (ordinary matter that interacts electromagnetically, thus visibly).

Noun

 * 1)  A hypothetical force of nature that acts on dark matter to allow dark matter to interact with itself.

Etymology 2
Dark being like black; "dark" being a metaphor for invisible (non-visible light)

Noun

 * 1)   ultraviolet light