Nyx without a male mate, and that her brothers were Moros ('Fate'), Hypnos ('Sleep') and Thanatos ('Death').
Generally, however, she is one of a group (Keres), as the Furies are. The name is usually derived from ker, 'destruction', 'doom', 'death', although it is more than likely that the word came from the name.
It seems to be a rare coincidence that these spirits have a name that resembles that of the Valkyries, the Scandinavian goddesses who conducted the slain from the battlefield to Valhalla (their palace of bliss), all the more as they were similar in nature.
But Valkyrie means 'chooser of the slain', from Old Norse valr, 'slain' (also the first element of Valhalla) and the root of kjösa, 'to choose', and this Old Norse word can hardly be linked, at any rate meaningfully, with the Greek one.