Nathum is the name of an Etruscan Underworld "demon" or "fury", Who, like Tuchulcha, is of rather indeterminate gender. Most authorities see Nathum as female, but Her frightful appearance can make it hard to tell. On one mirror-back, She is shown with Urusthe (the Greek Orestes) and Cluthumustha (Klytemnestra), menacing Orestes with a serpent. In the Greek legend, Klytemnestra, the sister of Helen, was forcibly wedded to King Agamemnon after he had murdered her first husband. She bore him a son, Orestes, and three daughters, among whom was Iphigenia. When the Greeks were stalled due to unfavorable winds and could not launch their assault on Troy, an oracle was consulted, who told them that Iphigenia must be sacrificed to the Goddess Artemis. This Agamemnon did, murdering his own daughter, and when the winds changed he set out for Troy. Klytemnestra, naturally enough, was not pleased with Agamemnon and when he returned from Troy several years later She promptly had him executed; some say her lover Aegisthos killed him, others that she did it herself with a double axe (an ancient symbol of the Goddess). This led to yet another killing down the road, that of Klytemnestra herself at the hands of her son Orestes, who was avenging his father (though not his sister, oh no). So: Klytemnestra was killed to avenge Agamemnon, who was killed to avenge Iphigenia, who was killed for a spot of good wind, who was the daughter of the guy who killed her mother's first husband. Got that? The Klytemnestra cycle reads as the clash between the original mother-right way of doing things and the later father-right way; proof of this is that Orestes was hounded by the Erinyes (Roman Furies) for the death of his mother, who punished him for the unforgivable crime of matricide.

In that complicated context, Nathum is shown as an Erinys hounding Urusthe/Orestes. Her identification with an Erinys adds further weight to seeing Nathum as female; for the Erinyes were not only themselves shown as female, but were especially associated with the punishment of crimes against women such as matricide. On this mirror-back, Nathum is very fierce-looking: Her hair stands on end, She has large teeth, and She carries a serpent like Tuchulcha. Her name is related to Etruscan natinusna or natinusnai, "demon". Probably in Her context of the Klytemnestra cycle, Nathum has been called a Deity of justice.